Simplify the tags input styles

After using them for a day the initial styles felt over done, so here are some small tweaks.

* Simplify the tags, no gradients or drop shadows.
* Use less padding to make them smaller.
* Remove the background color so they adopt the input background. This works nicely when the field loses focus.
* Increase the hit area of the delete button. It now takes up the entire right side of the tag.

![screen shot 2014-08-20 at 18 58 24](https://cloud.githubusercontent.com/assets/47144/3984868/964af5e4-288b-11e4-965c-032f9197f50e.png)