Updates and refactoring for 2DX-GL and Snap2D

-------Snap2D-------
-Refactored renderer libraries
    -Added com.snap2d.gl.spi to define common implementations accross Java2D/OpenGL rendering engines
    -com.snap2d.gl.opengl.GLHandle is now an interface with 2 working implementations, GL3Handle and GL2Handle
    -All inner types from GLHandle (except BufferUsage which remains implementation depenedent) have been moved to separate compilation units
-Refactored UI libraries
    -Removed com.snap2d.ui package
    -Renamed com.snap2d.ui.nifty -> com.snap2d.niftygui
-Refactored project libs folder and licenses
-OpenGL renderer now has working, fixed function compatibility profile for machines with minimum OpenGL 1.5
-Added automatic loading of configured GLProfile to GLConfig
-Removed "com." prefix from all GLConfig properties; so they now all look like snap2d.gl.opengl.*
-Fixed default shaders not working on Intel/AMD devices (hopefully) - added missing glBindVertexAttrib calls
-Changed all shader version declarations to "#version 150" - GLShader default version is also 150
-Added vertex attrib position binding APIs to GLProgram/GLShader
-Modified default/current program APIs in GLProgram
-GLShader now automatically prepends the snap2d-transform shader to ALL loaded vertex shaders, not just those loaded from Snap2D shader resource folder
-GLShader now also prepends the version declaration for vertex shader to allow for custom version specifications.
-Added com.snap2d.gl.opengl.res package and moved all Snap2D library default/test shaders there
-Removed SnapLogger in favor of using Java Logger utility
-Added com.snap2d.gl.ScreenUtils
-com.snap2d.gl.CrashReportWindow now displays "Unavailable" instead of -1 for system memory info when native libraries are not available

-------2DX-GL-------
-Removed Graphics2D instance variable and set/get methods in bg.x2d.Background (the code is old and faulty; storing Graphics2D objects is always a bad idea, so deprecation would have been useless)
-Fixed documentation in Background class
-Added bg.x2d.geo.LineSeg
-Added bg.x2d.utils.ConfigLogHandler
-Fixed bg.x2d.utils.Utils importing a Snap2D package

Updated README

commit build-id: b0000-183