Fix161 - Align rows of Params Panel and Timetrack Panel

- Add a CellRendererText to TimeTrackView with same font attribute
to have same rows height.
- Add a CellRendererPixbuf at end of TimeTrackView.
- Add initial support of alpha icon inside timetrack dock's treeview
- Add a gtk::drawingarea widget inside the timetrack dock's to align the time cursors
- Add utils_timetrack_align_icon.sif file
- Update icon procedure to include utils_timetrack_align_icon.sif
- Create icon stock icon for utils_timetrack_align_icon.sif
- Use the registred icon "utils_timetrack_align" in place of hard linked
- draw orange time cursor before graduation in timeslide widget
- Fix stock icon ID : synfig-utils_timetrack_align (synfig- was missing)