Performance improvements for 40M posts (#7708)

* Optimizing get root posts SQL query

* Setting session invalidation to be reliable

* Adding app reciever to SessionHasPermissionToUser

* Adding app reciever to SessionHasPermissionToTeam

* Adding app reciever to SessionHasPermissionTo

* Clear session cache if permission was denied

* Fixing rebase issues

* Revert "Optimizing get root posts SQL query"

This reverts commit f364757e7015cfb4ec673d0a4fc3d57cd25d8dd7.

* Fixing build

api4/reaction.go

@@ -7,7 +7,6 @@ import (
 	"net/http"
 
 	l4g "github.com/alecthomas/log4go"
-	"github.com/mattermost/mattermost-server/app"
 	"github.com/mattermost/mattermost-server/model"
 	"github.com/mattermost/mattermost-server/utils"
 )
@@ -92,7 +91,7 @@ func deleteReaction(c *Context, w http.ResponseWriter, r *http.Request) {
 		return
 	}
 
-	if c.Params.UserId != c.Session.UserId && !app.SessionHasPermissionTo(c.Session, model.PERMISSION_MANAGE_SYSTEM) {
+	if c.Params.UserId != c.Session.UserId && !c.App.SessionHasPermissionTo(c.Session, model.PERMISSION_MANAGE_SYSTEM) {
 		c.SetPermissionError(model.PERMISSION_MANAGE_SYSTEM)
 		return
 	}