Game Center/Guide overhaul for iOS 6+

Partially overhauled the Guide for iOS 6+ Game Center functionality:
Encapsulated repetitious code into single-purpose methods, fixed runtime
warnings for Game Center in iOS 7, and iOS 6+ no longer uses deprecated
methods to open Game Center windows (all compiler warnings in Guide.cs
are fixed). Also fixed a MatchMaker crash bug. Also fixed the formatting
(tabs, spaces, braces) in Guide.cs to be in line with MonoGame's coding
conventions. Bonus feature: Added access to iOS's Twitter API to the
Guide now too. Tested on iOS 5, 6, and 7.
Merge branch 'develop' of https://github.com/mono/MonoGame into develop

Conflicts:
	MonoGame.Framework/iOS/GamerServices/Guide.cs
Merge pull request #2504 from picobots/develop

Game Center/Guide overhaul for iOS 6+
Hooked up about and help items to website.
Fixed missing continue.
Added "Add Item" and "New Item" to the edit menu.
Added Total Items stats to project.
Added property grid attributes to project object.
Added property grid attributes to content and folder objects.
Fixed title of new project saving dialog.
We no longer close the project before creating the new one.
You can now cancel the content build.
Merge pull request #2509 from SickheadGames/pipeline4

More Pipeline GUI Improvements - Part 2
Hook up Javascript implementations to JSAPI class

To enable this to work, developers need to modify the default index.htm generated by Protobuild to have:

        manifests: [
          "MonoGame.Framework",
          "JSILPort.exe"
        ],

This will cause the appropriate MonoGame libraries to load.
Merge pull request #2517 from hach-que/web-api-working

Hook up Javascript implementations to JSAPI class
Implement game tick for Web platform

This hooks up the game's update and render loop for the Web platform, using
window.setTimeout to drive the loop behaviour.

Currently it always renders red when the graphics device is cleared, but this
is temporary.
Include JSAPIAccess in project definition
Merge pull request #2519 from hach-que/web-tick

Implement game tick for Web platform
GamerServices/Net are now deprecated.
Merge back from develop