Revert "remove <asset> from plugin.xml"

This reverts commit 102a60606754fc5bcdc33cc16ad5a21eb9e135c5.
the plugman hook + package.py now takes care of JS files
use new 'cleaner' plugman hook

rather than messy custom injectCordovaBlabla+xcodeproj+androidproj
Revert "Add GAPlugin again, this time as plain files."

This reverts commit c4b17116567b5613067ec4b1c99388f97a2a191a.
no need to 'maintain' files ourselves. submodule is better.
re-add GAPlugin as a submodule + bump version