on_load changes, renamed PM::ViewHelper to PM::Styling

This is fairly major, but should result in a really nice benefit.

* Moved the on_load to fire inside the loadView method. This will be more consistent than the previous implementation and allow developers to set up their views in `on_load` which feels more natural than `will_appear`.
* Renamed `PM::ViewHelper` to `PM::Styling`
* Added three helper methods (stolen from BubbleWrap) to `PM::Styling`: `hex_color(str)`, `rgb_color(r,g,b)`, `rgba_color(r,g,b,a)`. Sometimes you don't need all of BW but these are really helpful.