Improved Webpack support

[code418]

Amend the AMD references so that the library plugins can be used without any webpack config changes.

[janpaepke]

Could you amend these changes in the original source files instead of the dist, pls?

[janpaepke]

Thanks!
But I'm afraid I'll have to bother you again: Please exclude the dist files (/scrollmagic) from the pr, as they are only updated when a new version is released.

note to self: I should probably make this more clear in contributing.md

[janpaepke]

hey, thanks.
So I noticed this breaks the tests, which can't be a good sign.
I played around a little and noticed that it works, when I add
"scrollmagic": "ScrollMagic" at line 76 in dev/tests/main.js.

Unfortunately my experience with require or webpack aren't great, but I doubt this would be the right way to go about this, since the whole point of this was to make it work without additional configurations.
Do have any Idea why the tests may fail?

To run the tests use gulp test.
For more info see here:
https://github.com/janpaepke/ScrollMagic/blob/master/CONTRIBUTING.md#development-contribution