CPProgressIndicator fixes

- Make height 20px, same as in Xcode, so we can actually lay them out correctly without guessing. And they were just too tall at 25px anyway.

- In case the height does change in the future, calculate the correct height from the theme in NSProgressIndicator.

- Updated the theme descriptor to include the default height.

- Updated Aristo 2 PSD progress indicator artwork.

- Moved init of CPProgressIndicatorSpinningStyleColors out of layoutSubviews, it is file global and only needs to get done once.