Statusbar animation improvement + Activity Indicator View option

*note: The implementation/execution of Activity Indicator is bit sloppy IMO, but should do the job. Hopefully someone will fix it up. I felt that it was definitely needed, and also needed it for my project.

The appearing original statusbar seemed to be appearing without animation opposed to the disappearing topLabel. I hacked it a little to make it look more like the Mailbox app. I hope you like it. 

Also added some preprocessor directives for simpler adjustment of animation durations.