bugfix: div resize event bubbled up to window

As pointed out by Kai in
https://github.com/janpaepke/ScrollMagic/issues/180 jQuery events
bubble up by default.
This also concerned the „fake“ resize event for div containers.
Fixed now.
Update CONTRIBUTING.md
updated GSAP to most recent version

See https://github.com/janpaepke/ScrollMagic/issues/179
fixed: Error message with wrong loading order

See https://github.com/janpaepke/ScrollMagic/issues/182
added: adsense

Dear internet-god: please forgive me!
build v1.2.2