Merge pull request #11 from jcome/gtk-3

Show Cancel and Preview buttons on preview options dialog.
Improve tile rendering (group tiles into large rectangles)
Fix toolbar
Allow to link gorup origin to spline
Fix reverse manipulations for linked to spline objects
Fix middle button
Fix guidlines offset
Fix scrollbars for Timetrack Panel
Fix crash triggered by canvas switching (was introduced in previous commit)
Align height of timeslider to the Params TreeView header height. Use fixed size for keyframe list.
Fix scrolling for Timetrack Panel
Fix time cursor alignment
Change colors for Keyframe List widget
Use pref unit system for Spline(bline) tool option panel
Use pref unit system for some tools.

Including circle, draw, polygon, rectangle, star and width tools.
There are some other options which should use distance widget and
their unit should be inherit from setup dialog (user preferences).
Merge branch 'gtk-3' of https://github.com/blackwarthog/synfig into gtk-3