Added MaxTextureSize to GraphicsDevice

In XNA Textures can be larger than the screen (though there is a
maximum size) while in OpenGL they can't. This property returns the max
allowed. (for Windows DirectX it uses the XNA values to help porting)
Revert "Added MaxTextureSize to GraphicsDevice"

This reverts commit 1d064c458491815b2d9b868c13e07df1e35ec425.
Merge remote-tracking branch 'upstream/develop' into develop
[MonoMac] SaveAs* Implementations for MonoMac
Added info for the source versions of assimp/assimp-net binaries.
Minimal importer. Geometry doesn't look quite right yet.
Filled in missing content type methods.
Allowing texture name in sampler states using parenthesis.
Merge remote-tracking branch 'upstream/develop' into develop
Implemented some basic functionality for VertexContent.
Starting to implement minimal model processing.
Avoiding NullReferenceException with null Tag objects.
Model XNBs are writing, still some bugs.
Adding the unit and functional tests from the old submodule:

https://github.com/kungfubanana/MonoGame-Tests

Visit it for older change history.
Added hierarchy support
Fixed bug where shader from a previous pass could be assigned to the next pass.
Removed bogus assert on null shaders in EffectPass constructor.
Corrected vertex count calculation
Fixing hierarchy, some serialization changes.
After consulting the spec, this seems like a better fix for the NullReferenceException.