Whiteboard night mode

Modification of #481 to include night mode support for whiteboard icons, but with different icons. It would be nice to have a better "clear" icon, which won't be confused with "delete note", but I think this will do for now.

A script is included for generating all the icons for different modes and resolutions from the source illustrator file. The script is based on the official one provided in the action bar icon pack.

![normal](https://cloud.githubusercontent.com/assets/2818274/4415430/12eba9e8-452b-11e4-9585-3ffe0cfd2ce3.png)

![night](https://cloud.githubusercontent.com/assets/2818274/4415432/17cfa28e-452b-11e4-9d4f-1baefb2afddb.png)