Blender Git Loki

Add faster fprintf writer, remove unused headers

Changes here:

Reverted temporarily to std::vector to keep working, instead of
waiting for D7931 to get committed in master.

Adds an forced inline function for calculation of face/ polygon normals
by averaging vertex normals. I will look for an existing method.
This way, the allocated memory in `data_to_export->mvert[i].no` is
actually used.
Also, `BLI::Vector<uint> face_normal_index` is not needed anymore since
we loop over the same polygon list while writing normals, so
their indices will be the same.

Adds a writer method option, `fprintf`, which is faster than `fstream`.
With fstream, 478 MB of an ico-sphere with 8 subsurf takes 22 seconds.
with fprintf, the same takes 13 seconds.
With fstream, a 44 MB of cube with 8 subsurf take 2.3 seconds.
with fprintf, the same takes 1.4 seconds.

Adds timing info of the full export directly in console.

Removed unused and repeated headers from `wavefront_obj.cc`.

Differential Revision: https://developer.blender.org/D7959