Fix toolbarbutton hover and active states for Australis on Windows
Remove support for the old Firefox theme.

Change minVersion to 29.0.
Migrate fist run code to Customizable UI API.
Update Brief icon sizes to fit Australis requirements.
Use the same icons in the Add-ons Manager as in the UI.

The UI uses the same icon sizes as the Add-ons Manager now,
so instead of storing two copies of each, let's remove the
icons from the root directory and use install.rdf to point
to the /skin package.
Remove toolbar button migration code to Firefox 4
Adjust the glyph size of the 32x32 icon.
Adjust toolbar button appearance to Australis on Windows and Linux.

Make sure the button looks good in all possible areas: navigation
toolbar, other toolbars, tab bar, dropdown panel, and customization
palette. Because of the toolbar button's custom structure, we need to
copy and adapt CSS rules from the default theme and we need to do it
separately for each OS.
Bump version to 1.7.3