fix shade reference

[stewartyu]

Status: Ready to Merge Reviewers: @donnielrt @marlowpayne @mikenikles

Changes

• fixed Pikabu saving a reference to its Shade

  Todos:

• [ ] Engineer +1

  Known Bugs:

• using non-standard classes don't work (https://github.com/mobify/pikabu/issues/60)
• the Perspective effect has a Shade that's too skinny
• the Drawer effect has visual problems

  How to Test

• pull this branch
• npm install
• bower install
• grunt serve
• go to http://localhost:3000/examples
• try the Left or Right drawer effects
• it works!