Change: init Transferable only if the init function exists (compatibility
reasons)
New: CutCopyPasteTabs.Services added as Services.jsm is not present in
older versions of Firefox
Change: use CutCopyPasteTabs.Services instead of Services.jsm
Change: query restore_on_demand pref only if the pref exists
Change: min version supported shifted from Fx16.0 to Fx4.0
New: menuitems now listen to multiselectContextBroadcaster

The broadcaster is provided by the bug566510 addon (which is this addon's
dependency).
Change: removing handleEvent function and event listeners as they got
replaced by multiselectionContextBroadcaster.
Milestone: v1.0.4