[#2281] Added a TimeEntry#billable? method which is delegated to

TimeEntryActivity#billable?

init.rb

@@ -2,8 +2,10 @@ require 'redmine'
 
 # Patches to the Redmine core.
 require 'dispatcher'
+require 'overhead_time_entry_patch'
 require 'overhead_time_entry_activity_patch'
 Dispatcher.to_prepare do
+  TimeEntry.send(:include, OverheadTimeEntryPatch)
   TimeEntryActivity.send(:include, OverheadTimeEntryActivityPatch)
 end