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

templates/macros/widgets.html.twig

@@ -155,7 +155,7 @@
 {# for @internal use only #}
 {% macro label_color_dot(type, isVisible, name, url, color) %}
     {% apply spaceless %}
-    <span class="label-{{ type }}{{ isVisible ? '' : ' label-invisible' }}">
+    <span class="label-{{ type }}{{ isVisible is same as (false) ? ' label-invisible' : '' }}">
         <span class="name">
             <i class="dot {{ 'dot'|icon }} fa-fw"{% if color is not empty %} style="color:{{ color }}"{% endif %}></i>
             <span class="name-inner">