DOC: updated for the moving pictures tutorial 1.9.0 data

~~**NOT READY FOR MERGE**~~

Various updates, including:
 * collapsing all inputs into a single fastq file (which is a more common use case than multiple fastq files)
 * use of the ``--recover_from_failure`` option for ``core_diversity_analyses.py`` to add categorical analyses (a big time saver that users should be aware of)
 * addition of time axis to Emperor plots
 * improved naming of some of the metadata in the mapping file
 * addition of some recent references
 * some text and code clean-ups

~~Working on some strange clustering of samples - it's possible that I have some mislabeling here.~~
Can you add an explanation before this cell? It isn't clear why you're running core_diversity_analyses.py twice.