WIP: Popup Support

My work-in-progress branch for popup dialog support in Ionic.

- [x] Configure size of window
- [x] Return promise for showPopup
- [x] Directive or not (let user put popup in dom, or just through service?)
  - I've decided to allow loading popup content from a template if they want
- [x] add `ion` prefixes
- [x] Evaluate popupView
- [x] Saving the popup not necessary?
- [x] Properly handle things like form fields, etc
- [x] Pop-in animation for grade-A platforms
- [x] Support for quick wrapping of `alert`, `prompt` and `confirm`
- [x] Don't duplicate popup backdrop
- [x] Remove, don't just hide
- [x] Support handling hide/remove from inside the service to hide backdrop
- [x] Document that shit in the spirit of mr joslin
- [x] Somehow pass data back from arbitrary popups, or let the user somehow configure this?
- [x] Hide until ready to show
- [x] Unit test that shit