More db changes

Changes:
 - Added analysis_chain table to analysis group. Keeps track of the analysis network as discussed today with @wasade @adamrp @josenavas 
 - Added analysis_filepath table to analysis group. Links an analysis with its filepath entry in the main filepath table. (Mainly biom tables)
 - Added job_results_filepath to analysis group. Links a job with the resulting filepath entries in the main filepath table. 
 - Added study_preprocessed_data table to link a study with it's preprocessed data entry. Needed because one raw data file can belong to multiple studies.
 - Heavily rearranged schema to make it pretty :smile: