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

api/context.go

@@ -26,9 +26,9 @@ type Context struct {
 	IpAddress    string
 	Path         string
 	Err          *model.AppError
+	siteURL      string
 	teamURLValid bool
 	teamURL      string
-	siteURL      string
 	T            goi18n.TranslateFunc
 	Locale       string
 	TeamId       string