activity: basic query support

only supports queries of fields actually in Activity. The web UI only
directly queries two of these, ID and Time (mistakenly referneced as date in
the web ui previously). Later commits will come up with creative ways of
dealing with all the other query types.

models.go

@@ -175,10 +175,6 @@ type PaginatedReqDTO struct {
 	Ascending   bool   `json:"ascending"`
 }
 
-type getUsersReqDTO struct {
-	ServerSearchReqDTO
-}
-
 type getUsersDTO struct {
 	UserList []*respUser `json:"users"`
 	LastPage bool        `json:"last_page"`
@@ -445,12 +441,6 @@ type ActivityDTO struct {
 	IP             string `json:"ip"`
 }
 
-type GetActivitiesDTO struct {
-	// "SortByField" ignores, it's always time.
-	PaginatedReqDTO
-	Type []string `json:"type"` // Types of activity to get. Leave blank for all.
-}
-
 type GetActivitiesRespDTO struct {
 	PaginatedDTO
 	Activities []ActivityDTO `json:"activities"`