Migrate functions to app package (#5106)

* Refactor and move session logic into app package

* Refactor email functions into the app package

* Refactor password update into app package

* Migrate user functions to app package

* Move team functions into app package

* Migrate channel functions into app package

* Pass SiteURL through to app functions

* Update based on feedback

app/session_test.go

@@ -22,7 +22,7 @@ func TestCache(t *testing.T) {
 		t.Fatal("should have items")
 	}
 
-	RemoveAllSessionsForUserId(session.UserId)
+	ClearSessionCacheForUser(session.UserId)
 
 	rkeys := sessionCache.Keys()
 	if len(rkeys) != len(keys)-1 {