Update toolbar customization to be compatible with the Firefox Australis theme

Review: http://codereview.adblockplus.org/5741004535627776/
Slightly simplified backwards compat toolbar customization code.

Review: http://codereview.adblockplus.org/5741004535627776/

--HG--
extra : rebase_source : 93fd14db5bd14e8ebbcc9a884bc6c6d918a02947
Fixed event handlers on toolbar icon (only relevant if defaulttoolbaraction pref was changed)

Review: http://codereview.adblockplus.org/5741004535627776/

--HG--
extra : rebase_source : 7f84f249ae170b8229ffa3e1b61906c56f3df2b4
Updated copyright year
Issue 186 - Disabled ABP icon in toolbar re-appears after SeaMonkey restart
Issue 427 - Remove non-standard function and getter syntax
Backed out changeset 2d52467436ed (Issue 427 - Remove non-standard function and getter syntax) - dropping compatibility with Firefox 21 and below wasn't intentional
Relanded changeset 2d52467436ed (Issue 427 - Remove non-standard function and getter syntax) with appropriate compat info changes