Feature/popup appearance

This PR adds the ability to switch the appearance of the Popop between NSPopoverAppearanceMinimal (Default) and NSPopoverAppearanceHUD.

* NSPopoverAppearanceMinimal - NSPopover Default 
![screen shot 2014-09-01 at 11 09 19](https://cloud.githubusercontent.com/assets/900594/4106469/48ba69f8-31ba-11e4-961b-06b335475dd5.png)

* NSPopoverAppearanceHUD
![screen shot 2014-09-01 at 11 09 28](https://cloud.githubusercontent.com/assets/900594/4106468/48b60930-31ba-11e4-8e7c-83f0c62b8870.png)