accounts: fix bool queries on (some) string fields

wasn't implemented for things like email on the server side.
also changed text mail variant's footers to all use {{ .footer }} like I
should have before.

mail/confirmation.txt

@@ -5,4 +5,4 @@
 
 {{ .confirmationURL }}
 
-{{ .message }}
+{{ .footer }}

mail/created.txt

@@ -6,4 +6,4 @@
 
 {{ .timeString }}: {{ .time }}
 
-{{ .notificationNotice }}
+{{ .footer }}

mail/deleted.txt

@@ -4,4 +4,4 @@
 
 {{ .reasonString }}: {{ .reason }}
 
-{{ .message }}
+{{ .footer }}

mail/expired.txt

@@ -2,4 +2,4 @@
 
 {{ .expiredAt }}
 
-{{ .notificationNotice }}
+{{ .footer }}

mail/expiry-adjusted.txt

@@ -8,4 +8,4 @@
 
 {{ .reasonString }}: {{ .reason }}
 
-{{ .message }}
+{{ .footer }}

mail/expiry-reminder.txt

@@ -2,4 +2,4 @@
 
 {{ .yourAccountIsDueToExpire }}
 
-{{ .message }}
+{{ .footer }}

mail/invite-email.txt

@@ -5,4 +5,4 @@
 
 {{ .inviteURL }}
 
-{{ .message }}
+{{ .footer }}

mail/password-reset.txt

@@ -10,4 +10,4 @@
 
 {{ .pinString }}: {{ .pin }}
 
-{{ .message }}
+{{ .footer }}

mail/template.txt

@@ -1,3 +1,3 @@
 {{ .plaintext }}
 
-{{ .message }}
+{{ .footer }}

mail/user-expired.txt

@@ -2,4 +2,4 @@
 
 {{ .contactTheAdmin }}
 
-{{ .message }}
+{{ .footer }}

mail/welcome.txt

@@ -8,4 +8,4 @@
 
 {{ .yourAccountWillExpire }}
 
-{{ .message }}
+{{ .footer }}

usercache.go

@@ -345,9 +345,19 @@ func (q QueryDTO) AsFilter() Filter {
 			return cmp.Compare(strings.ToLower(a.Name), strings.ToLower(q.Value.(string))) == int(operator)
 		}
 	case "email":
+		switch q.Class {
+		case BoolQuery:
+			return func(a *respUser) bool {
+				if q.Value.(bool) {
+					return a.Email != ""
+				}
+				return a.Email == ""
+			}
+		case StringQuery:
 			return func(a *respUser) bool {
 				return cmp.Compare(strings.ToLower(a.Email), strings.ToLower(q.Value.(string))) == int(operator)
 			}
+		}
 	case "notify_email":
 		return func(a *respUser) bool {
 			return cmp.Compare(bool2int(a.NotifyThroughEmail), bool2int(q.Value.(bool))) == int(operator)
@@ -391,17 +401,37 @@ func (q QueryDTO) AsFilter() Filter {
 			return cmp.Compare(bool2int(a.Disabled), bool2int(q.Value.(bool))) == int(operator)
 		}
 	case "telegram":
+		switch q.Class {
+		case BoolQuery:
+			return func(a *respUser) bool {
+				if q.Value.(bool) {
+					return a.Telegram != ""
+				}
+				return a.Telegram == ""
+			}
+		case StringQuery:
 			return func(a *respUser) bool {
 				return cmp.Compare(strings.ToLower(a.Telegram), strings.ToLower(q.Value.(string))) == int(operator)
 			}
+		}
 	case "notify_telegram":
 		return func(a *respUser) bool {
 			return cmp.Compare(bool2int(a.NotifyThroughTelegram), bool2int(q.Value.(bool))) == int(operator)
 		}
 	case "discord":
+		switch q.Class {
+		case BoolQuery:
+			return func(a *respUser) bool {
+				if q.Value.(bool) {
+					return a.Discord != ""
+				}
+				return a.Discord == ""
+			}
+		case StringQuery:
 			return func(a *respUser) bool {
 				return cmp.Compare(strings.ToLower(a.Discord), strings.ToLower(q.Value.(string))) == int(operator)
 			}
+		}
 	case "discord_id":
 		return func(a *respUser) bool {
 			return cmp.Compare(strings.ToLower(a.DiscordID), strings.ToLower(q.Value.(string))) == int(operator)
@@ -411,17 +441,37 @@ func (q QueryDTO) AsFilter() Filter {
 			return cmp.Compare(bool2int(a.NotifyThroughDiscord), bool2int(q.Value.(bool))) == int(operator)
 		}
 	case "matrix":
+		switch q.Class {
+		case BoolQuery:
+			return func(a *respUser) bool {
+				if q.Value.(bool) {
+					return a.Matrix != ""
+				}
+				return a.Matrix == ""
+			}
+		case StringQuery:
 			return func(a *respUser) bool {
 				return cmp.Compare(strings.ToLower(a.Matrix), strings.ToLower(q.Value.(string))) == int(operator)
 			}
+		}
 	case "notify_matrix":
 		return func(a *respUser) bool {
 			return cmp.Compare(bool2int(a.NotifyThroughMatrix), bool2int(q.Value.(bool))) == int(operator)
 		}
 	case "label":
+		switch q.Class {
+		case BoolQuery:
+			return func(a *respUser) bool {
+				if q.Value.(bool) {
+					return a.Label != ""
+				}
+				return a.Label == ""
+			}
+		case StringQuery:
 			return func(a *respUser) bool {
 				return cmp.Compare(strings.ToLower(a.Label), strings.ToLower(q.Value.(string))) == int(operator)
 			}
+		}
 	case "accounts_admin":
 		return func(a *respUser) bool {
 			return cmp.Compare(bool2int(a.AccountsAdmin), bool2int(q.Value.(bool))) == int(operator)