GanttCalendarPlugin: cleanup `ganttcalendar/ticketgantt.py`


git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@844 456a77e7-5939-0410-b211-84f85430c667
GanttCalendarPlugin: simplify verbose code


git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@845 456a77e7-5939-0410-b211-84f85430c667
GanttCalendarPlugin: file names of template have `ganttcalendar_` prefix


git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@846 456a77e7-5939-0410-b211-84f85430c667
GanttCalendarPlugin: allow sorting with any field in gantt chart (sf.jp #34214)


git-svn-id: http://svn.sourceforge.jp/svnroot/shibuya-trac/plugins/ganttcalendarplugin/trunk@847 456a77e7-5939-0410-b211-84f85430c667