[wip/assimp] Upgrade to 3.0.1270

Changes since 2.0:

FEATURES:
	- new export interface similar to the import API.
	- Supported export formats: Collada, OBJ, PLY and STL
	- added new import formats: XGL/ZGL, M3 (experimental)
	- new postprocessing steps: Debone
	- vastly improved IFC (Industry Foundation Classes) support
	- introduced API to query importer meta information (such as
	  supported versions, full name, maintainer info).
	- reworked Ogre XML import
	- C-API now supports per-import properties

FIXES/HOUSEKEEPING:

	- hundreds of bugfixes in all parts of the library
	- unified naming and cleanup of public headers
	- improved CMake build system
	- templatized math library
	- reduce dependency on boost.thread, only remaining spot
	is synchronization for the C logging API

API COMPATIBILITY:
	- renamed headers, export interface, C API properties and meta data
	  prevent compatibility with code written for 2.0, but in most cases
	  these can be easily resolved
	- Note: 3.0 is not binary compatible with 2.0