Instantiation of objects from appleseed.studio

User is able to instantiate an object by right-clicking on it and
selecting "Instantiate...". The instance has a default pose and
no materials assigned to it.
Write OSL shaders in ProjectFileWriter.
Removed wrong comment.
Merge pull request #325 from est77/OSL_work

Write OSL shaders in ProjectFileWriter.
minor cleanups.
bug 321: fixing minor issues
Merge pull request #324 from marius-avram/B312

Instantiation of objects from appleseed.studio
added todo notes (related to issue #327).
building appleseed with SSE/SSE2 instruction sets on 32-bit Linux is no longer supported.