Upgrade to BubbleWrap 1.5.0

Hey,

I did 4 things:
1. I changed the gemspec to require BubbleWrap 1.5.0
2. In the StatusBar::Base `initialize` method I got rid of the `return` statement within the timer block since it causes an error. This describes the problem the best: http://goo.gl/0NnUAy
3. In `lib/status_bar.rb` I added a require statement to require `sugarcube` in it's entirety. Without it `SugarCube::CoreGraphics` wouldn't be present.
4. I bumped the version to 0.2.4

I tested the changes with BW 1.5.0 as well as 1.4.0, both work for me just fine.

Cheers
- Chris