LibThree Beta 6 released

After some delay, the new Beta 6 is out which focuses on usability improvements.

[New features]
 * added tangent and material id render channels
 * the real-time renderer now supports most render channels
 * added lasso selection (with the Crtl key)
 * GUI keyboard navigation
 * check for updates on startup
 
[Modified features]
 * faster normal and tangent generation with subdivision of animated blend shapes/alembic
 * added anisotropy to the toon shader
 * support output file name keywords like ####, <camera>, <date>, etc
 * reworked the "save" button to allow manual saving of the current changes
 * added new button that reverts the scene to the last saved state
 * show save icon after an automatic backup
 
[Bug fixes]
 * fixed various issues of the real-time renderer with the toon material
 * fixed issues related to skeletal deformers
 * fixed issues related to tangent generation
 * fixed GLSL shader failure with solid color environment
 * fixed "#include nested too deeply" GLSL error on NVIDIA cards
 * fixed issue with the GLSL shader cache on NVIDIA cards, causing unnecessary shader recompilation
 * the real-time engine was ignoring the scale of the light's node, unlike the photoreal engine
 * fixed assignment of multiple materials to blend and skeletal deformers
 * fixed rare crash while sampling the environment texture
 * fixed rare mipmap filtering issue with the photoreal renderer.
 * fixed issues with "Use viewport resolution"