use backend before importing pyplt
Install LaTeX for integration tests
Merge pull request #465 from elehack/feature/elehack-cleanup

Merge in Michael's cleanups and new fixes.
Improve test logging
Factor out the SVD model
Refactor FunkSVD item scorer in prep for SVD scorer
Make ImmutableVec.create variadic
Introduce biased MF kernels
Add sub-vector support to vectors
Initial matrix classes (refs #333)