storage: user set/get methods for contact method access

Get/GetKey/SetKey/DeleteKey methods are used for access to
email/discord/telegram/matrix, everywhere. Mutex added for each, avoids
concurrent read/write issues. Will also make potential transition to
database easier.

auth.go

@@ -209,7 +209,7 @@ func (app *appContext) getTokenLogin(gc *gin.Context) {
 		if !app.config.Section("ui").Key("allow_all").MustBool(false) {
 			accountsAdmin := false
 			adminOnly := app.config.Section("ui").Key("admin_only").MustBool(true)
-			if emailStore, ok := app.storage.emails[jfID]; ok {
+			if emailStore, ok := app.storage.GetEmailsKey(jfID); ok {
 				accountsAdmin = emailStore.Admin
 			}
 			accountsAdmin = accountsAdmin || (adminOnly && user.Policy.IsAdministrator)