Template tags to add bower installed files automatically.

[tjwalch]

I created a template tag library that let's you include bower installed files automatically if the bower.json file includes a proper "main" section.

I opened this pull request just to show it and get comments on whether this is a good feature to include in the main repository. If so it needs to be updated with tests and documentation, something I wont be writing just for me :)

[nvbn]

Thanks!