Corrected color bug with SaveAsJpeg on Windows Phone 8

Adjusted the Windows Phone 8 version of Texture2D's SaveAsJpeg class to
switch the pixels RGBA/BGRA values so that Writeablebitmap will read the
data correctly.  Added helper function in Texture2D called ConvertToRGBA
to convert the pixel data.  Images now save as properly colored JPEGs.
Moved pixel format conversion off "UI Thread".
Build MonoGame.Framework.Content.Pipeline on supported platforms.
Removed excess assignment of the G and A Pixels.
Build MonoGame.Framework.Content.Pipeline on supported platforms.
Merge remote-tracking branch 'origin/_pm/build-content-pipeline' into _pm/build-content-pipeline
Merge pull request #2051 from PrecisionMojo/_pm/build-content-pipeline

Build MonoGame.Framework.Content.Pipeline on supported platforms.
Merge pull request #2068 from dellis1972/develop

Updated Addin build script to build linux addin
Implementation of Matrix.CreateShadow()

Implementation of Matrix.CreateShadow()
Merge pull request #2029 from Strifex/develop

Corrected color bug with SaveAsJpeg on Windows Phone 8
Merge pull request #2072 from nkast/tnc_Matrix_CreateShadow

Implementation of Matrix.CreateShadow(...)