Added capability for hair export as geometry.  Exports as .obj for now, but the functionality is there for testing for and writing particle systems.  All that's needed is to replace the .obj geometry export with Alembic curve cache.
-Fixed material UI bug with specular BTDF.
-Fixed bug: not writing node textures correctly to BSDF reflectances.
Added support for particle / dupli- instance motion blur
Added support for textured spotlights
Also added properties to lamps, added them to UI
Fixed .appleseed file-only export operator
Fix for particle systems: two particle systems on the same object, only one rendered.
There is still unpredictable behavior for multiple particle systems when motion blur is enabled.
Some code cleanup
Added render layer functionality, actually exports per-object render layer assignments now, but very primitive implementation
Added operator to assign selected objects to / remove selected objects from currently selected render layer
Added Cython files to gitignore
Fixed some label names
Merge pull request #15 from est77/est_label_fixes

Label fixes and other small changes
Added tile ordering property
changed some UI elements