event-editor: Create GcalTimeChooserRow

Create a new GcalTimeChooserRow widget from AdwEntryRow that parses the
entry into a time, or lets the user pick a time from a popover.

[feaneron] Improved code style, reworked regex management.

src/gui/event-editor/event-editor.gresource.xml

@@ -11,6 +11,7 @@
     <file compressed="true">gcal-reminders-section.ui</file>
     <file compressed="true">gcal-schedule-section.ui</file>
     <file compressed="true">gcal-summary-section.ui</file>
+    <file compressed="true">gcal-time-chooser-row.ui</file>
     <file compressed="true">gcal-time-selector.ui</file>
   </gresource>
 </gresources>