Add culture harvest date and date obtained

Add these two data points to biosample search output.
Merge branch 'master' of https://github.com/ENCODE-DCC/encoded into 2424-biosample-search
Merge remote-tracking branch 'origin/master' into 2424-biosample-search
Merge remote-tracking branch 'origin/master' into 2424-biosample-search
Merge pull request #493 from ENCODE-DCC/2424-biosample-search

2424 Add fields to biosample search results