Adding in support for UIProgressView
Refactored UIProgressView code, standardized Progress's property names
Updated podspec to 0.2.7
Fix the conditionals for bypassing the rendering of UIView

Suggested by @christophercotton. Fixes #105
UISwitch and UISlider would not render subclasses even if the nuiClass was exlicitly set
Merge pull request #106 from christophercotton/master

Make UISwitch and UISlider render subclasses correctly