More app code migration (#5170)

* Migrate admin functions into app package

* More user function refactoring

* Move post functions into app package

app/session.go

@@ -6,7 +6,6 @@ package app
 import (
 	"github.com/mattermost/platform/einterfaces"
 	"github.com/mattermost/platform/model"
-	"github.com/mattermost/platform/store"
 	"github.com/mattermost/platform/utils"
 
 	l4g "github.com/alecthomas/log4go"
@@ -124,15 +123,6 @@ func AddSessionToCache(session *model.Session) {
 	sessionCache.AddWithExpiresInSecs(session.Token, session, int64(*utils.Cfg.ServiceSettings.SessionCacheInMinutes*60))
 }
 
-func InvalidateAllCaches() {
-	l4g.Info(utils.T("api.context.invalidate_all_caches"))
-	sessionCache.Purge()
-	ClearStatusCache()
-	store.ClearChannelCaches()
-	store.ClearUserCaches()
-	store.ClearPostCaches()
-}
-
 func SessionCacheLength() int {
 	return sessionCache.Len()
 }