BeginShowKeyboardInput fixed for iOS
Remote status bar hiding from this tag as it needs to be discussed
Merge branch 'develop' of https://github.com/mono/MonoGame into ioskeyboardfix

Conflicts:
	MonoGame.Framework/MonoGame.Framework.iOS.csproj
Remove iOS csproj in favor of Protobuild
Updated Protobuild definition
Add support for loading indexed image files into a texture through Texture2D.FromStream.
Fix bug where GraphicsDevice.Clear() always cleared stencil and depth buffers.

This was a consequence of moving platform-specific code that prior to
eeafc23378861d1401ebdba417431b4e850e8abf only ran for the single-parameter
form of Clear() into a PlatformClear() method used by all forms of Clear().

This change splits it out again.
Add PlayStation4 to content pipeline target platforms.
Removed preshaders which we don't support.
Removed unused GLSLOptimizer class.
Fixed assembly info.
Removed some unused stuff.
Moved EffectObject to TwoMGFX namespace.
Moved HLSL compile step to CompileHLSL.
Cleaned up a bunch of redundant namespace qualifications.
Added placeholder for CompilePSSL.
Fixed namespacing to TwoMGFX for now.
Added missing source files.
Added dummy ShaderData.CreatePSSL method.
Merge pull request #2346 from SickheadGames/refact_mgfx

More MGFX Tool Refactors
Merge pull request #2260 from Nezz/ioskeyboardfix

BeginShowKeyboardInput fixed for iOS
Allow full path to external tools & attempt to address some cross-platform inconsistencies.
Update README.md

Fixed links to new build server.