[Atom] Create Atom Plugin

[rageandqq]

Created an atom plugin! Woo! Follows the protocol defined in the Wiki.

Added a similar dev setup script with symlinks. You will however need to install the required node modules before this will work.

Granted, this isn't launch blocking, so don't feel rushed to review.

Will add screenshots/screencasts here as well.

https://github.com/geoffxy/tandem/issues/30

[rageandqq]

This is now additionally out of date. Changes similar to those in https://github.com/geoffxy/tandem/pull/97 will need to be added to support the hole punching updates.

[todrobbins]

Excited to see this piece finished! Thanks for the hard work!