Delete Dialog tweaks

Styled Delete dialog fragment to comply with Material Design guidelines (http://www.google.com/design/spec/components/dialogs.html#dialogs-usage)

I think borderless buttons are visually better and the red color for DELETE button enhances the 'danger' feeling.

P.S: Is there a little UI problem with the dialog header or is just me?
![device-2014-07-10-210127](https://cloud.githubusercontent.com/assets/8081613/3543693/b78f2280-0864-11e4-9c85-9ecc946b7432.png)