Stage 1: Remove fit, fitmultilevel, benchmark.

Also: dependency on scikit-learn is no longer needed in core.
remove modeldriven
remove DX, DP, DL, modelinstance
remove SimilarityModel2D, fixes for diff subclassing
add master channel to CI
Merge pull request #499 from jabooth/rmfit

spin out AAM, CLM, SDM, ATM and related code to menpofit