Update Linux build script for Ubuntu 14.10
Glib 2.42 fixes : Parameters are not editable

I was "force" to add a preprocessor directive due to glib changes...

Saying that, now we must build and ship for OS coming with glib >= 2.42
Fix glib version condition
Fix #715: Glib 2.42 issue for keyframes list. Thanks to Ron Bentley.

See http://www.synfig.org/issues/thebuggenie/synfig/issues/715
Always use "By Layer Default" blend method on startup.

This allows to avoid the confusions when (nebbie) user accidentaly changes the default blend method to something like "Divide". In this case the user will be wondering why nothing appears on the scren when he creates something. With this change the blend method will be reset to default value when application is restarted.
Use pixels as default unit of measurement (closes #710)

http://www.synfig.org/issues/thebuggenie/synfig/issues/710
Use "Frames" as default time format
Linux build: Add GTK3 support for packaging script
Brush tool : Autoresizable Brush chooser as Gtk::ToolPalette

* Remplace Gtk::Box by Gtk::Grid as main container (Gtk::Grid is a new widget that'll replace Gtk::Box)
* Remplace Gtk::Grid by Gtk::ToolPalette for brushes container
* Remplace Gtk::RadioButton by Gtk::RadioToolButton
ToolBox : Propagate Scroll Event from Palette

Make the Tool Palette scrollable from inside the palette not just from the scrollbar
Brush tool : Replace RadioToolButton by ToggleToolButton

Active brush was no-efficient + constitency ui with ToolBox

* Convert all RadioToolButton ref to ToggleToolButton
* Remove unuseful Gtk::RadioToolButton::Group references
* Use of StateBrush_Context::selected_brush_button to track previous selected brush