refactor simulator screen

big refactoring on the prosthesis side focused on the screen simulation components,
window resizing and "gaia window management tweaks".

- remove any DOM related code from the GlobalSimulatorScreen javascript module
- propagate orientation change to visible windows using mozilla parent-child messaging
- new screen orientatio change listener implementation (from DOMFMRadioChild)
- relaunch app if already running (prevents iframe leaking due to rapid kill+run sequence)
- fix app orientation on b2g-desktop not already running
- isolated DOM related code into prosthesis/content/window_manager.js
- use mutation_summary.js to detect changes in the gaia app iframes dom elements list

should fix #346