Fix stencil clear

Some drivers (especially on Android) will obey the stencil test when clearing the stencil buffer (the specs says it shouldn't). This workaround ensure that the stencil buffer will properly be cleared.
Added missing semicolon
Removing assert Pow2 from Texture.GetPitch. It is not appropriate to have this assert in the base Texture.cs file because it is platform specific whether or not this is actually a valid constraint and area already doing their own dimension validation.
Merge branch 'develop' of https://github.com/SickheadGames/MonoGame into develop
Merge pull request #2482 from prollin/patch-1

Fix stencil clear
Now using FreeImage to import Textures on Windows.
Added support for more types within EffectMaterialReader
Fixed import behavior.
"Compile Include" items are imported as /build items.
"Content Include" items with a CopyToOutputDirectory value other than Never are imported as /copy items.
Added missing Microsoft.Xna.Framework.Graphics exceptions.
Changed SerializableAttribute to DataContract so it can compile on all platforms.
Updated TextureImporter with all of the file types that FreeImage supports.
Feeble attempt at formatting the massive amount of RAW image formats.
Fix for issue #1745
VertexDeclarationReader.cs now enabled for all platforms
Merge pull request #2486 from SickheadGames/DeviceLostException

Added Missing Microsoft.Xna.Framework.Graphics Exceptions
Merge pull request #2485 from SickheadGames/FreeImageSupport

FreeImage TextureImporter Support
OK, I've tested the two following helper classes against all the platforms with the necessary #if's to unify all file and reflection requirements by the solution

* Utilities - FileHelpers.cs - built from all the references / code snippets for files used throughout the codebase in to a single class
Centralised helper classes for #1640
(Only changes that are included is a renamed GetFilename function and other minor changes suggested by @tomspillman)

* Utilities - ReflectionHelpers.cs - built from all the references / code snippets for reflection used throughout the codebase in to a single class

Note all code present in the classes come directly from implementations in the MG codebase.  No new additions added (unless is was for refactoring)

Next step is to replace current implementations (moved to these classes) in the MG codebase and get rid of a whole load of #ifs
Merge pull request #2487 from DDReaper/#1745_fix

Fix for issue #1745
Add an error for platforms that can't use Game.Exit()
Also include iOS
Route around calling main Game class' close method.