Cask for ShadowSweeper

ShadowSweeper disables drop shadows on windows, useful with tiling
managers such as Slate or SizeUp. Insanity's ShadowKiller is more
widely used, but now deprecated and not available from their page
anymore.
Merge pull request #1176 from maebert/master

Cask for ShadowSweeper
Add twitterrific 4.5

Add twitterrific app - beautiful twitter client.
Merge pull request #1177 from lucmendelowski/twitterrific

Add twitterrific 4.5
Add Choosy
Merge pull request #1179 from jimbojsb/choosy

Add Choosy