Menubar image, timer image and clock image turned into templates

Was annoyed by the fact that the Tomighty menu bar icon was invisible as per #14 so I made a quick fix. You just need to set the images as templates and they will render correctly in both modes.

Tested on OS X 10.10.1:

![Normal Mode](https://cloud.githubusercontent.com/assets/738351/5377500/979604ce-807a-11e4-9910-393f43c3aa99.png)

![Dark Mode](https://cloud.githubusercontent.com/assets/738351/5377502/991564ac-807a-11e4-9e3f-2e3e76ff82cf.png)