Added hover animation with box-shadow

Now on another branch.
Update per code review

removed unnecessary vendor prefix rule; moved :hover and :active inside .afch-button block due to nested rules in LESS
Further update per code review

Merged rules into `.gradient-button` class; differentiated normal and
`:active` states
Fix misaligned whitespace

Tabs, not spaces!
Tone down gradient on hover/active

0.2 changed to 0.1
Merge pull request #14 from WPAFC/box-shadow-hover

Added hover animation with box-shadow; toned down gradient