prepare release 1.15 (#2707)

* bump version
* fix invisible class on labels
* fail safe removal of foreign key
* check if optional form field exists before accessing it
* silently ignore stopped timesheets
* prevent colliding parameter names
* make sure decimal duration is always rendered with two decimals
* simplify translation
* fix #2751 ANSI_QUOTES
* rename composer task
* fix billable statistic rates
* added missing translation for export

src/Constants.php

@@ -25,7 +25,7 @@ class Constants
     /**
      * The current release status, either "stable" or "dev"
      */
-    public const STATUS = 'dev';
+    public const STATUS = 'stable';
     /**
      * The software name
      */