start/stop tracking: issue context menu entry

app/views/stopwatch_issue_timers/start.js.erb

@@ -1,4 +1,5 @@
 <% if @started_time_entry %>
+  contextMenuHide();
   window.stopwatch.timerStarted(
     <%= raw Stopwatch::Timer.new(User.current).to_json %>
   );

app/views/stopwatch_issue_timers/stop.js.erb

@@ -1,3 +1,4 @@
+contextMenuHide();
 window.stopwatch.updateStartStopLink(
   '#stopwatch_stop_timer_<%= @issue.id %>',
   '<%= j Stopwatch::IssueLinks.new(@issue).start_timer %>'