Remove old precalculated files

Note this is only a soft removal and permanently removing them later should be a priority to help reduce the size of the repository.
Update documentation for new precalculated files

Added doc page with list of all precalculated files from each gg version.

Added extra information to install doc about having to download precalc files.

Added new options for choosing gg version and type of function for the metagenome_prediction tutorial.
Update options for gg version and functional types

Add gg_version 13_5 and make it default.
Add rfam as another type of prediction.
Update version from 0.9.1-dev to 0.9.2
Add picrust/data/* to .gitignore
Remove unneeded import statement
Update automated script documentation.
Update metagenome_contributions.py to load new precalc files