[#16] Use add-on SDK.
Remove xul-overlay based code.
Use page-mod module for showing sticky views.
Use sidebar mudule and reuse sidebar.xul, Sidebar.js, sidebar_overlay.js
[#16] Remove sidebar_overlay.js -> sidebar_main.js
[#16] Fix tagbox placeholder
Fix error when Sidebar directory tree item is double clicked
[#16] Remove warining: don't use deprecated moudle pathes
[#16] Migrate unit-test
[#16] Refactoring DAO -> DBHelper
[#16] Implement addon-bar menu
[#16] Use l10n text on context script
addon code send strings by self.port.emit