Include injection grammars in active list

I had been noticing a flicker sometimes when reopening Atom with open editors, tracked it down to files that had injection selector matches since previously we weren't store injection selector grammars in the active list.

Show below is a GIF of the issue, I'm refreshing and you notice the flicker after it reopens, caused by the hyperlink on the first line causing a re-tokenizing.

![injection-flicker](https://cloud.githubusercontent.com/assets/671378/4158142/330378ae-3488-11e4-9f79-5cf9265d8d14.gif)