Created common exec proxy module

Since windows8 and firefox both used the exact same module
(commandProxy) I refactored this to a common/exec/proxy module.

I left the original commandProxy modules in for old plugin support
but will now log to the console to point to the new module.
Set VERSION to 3.3.0-dev (via coho)
CB-5247 [BlackBerry10] Map blackberry.event to document
CB-5247 [BlackBerry10] Map blackberry.event to document
CB-5253 remove webworks.exec
CB-5253 remove webworksready event
CB-5307 Remove references to Callback and Incubator
CB-5334 [BlackBerry10] Add command proxy to exec