Make Tweaks.js more simple

Changes:

1. New tweak's types: stylesheet, attributes.

2. Use new types for existing tweaks.

3. CustomizationMode.js (code for adding link).

4. Remove sizeModeChange event listeners.

5. Small code fixes.
Change type of urlbarHistoryDropmarker tweak to attribute
Upgrade to Firefox 29.0 beta 9
Merge branch 'master' into new-style-tabs

Conflicts:
	extension/include/Tweaks.js