Merge pull request #22 from felixeye/master

Help message for collaborators name. fixes #21
Add ContentType listing in Admin. Update documentation. Fixes #5
Merge pull request #23 from inodb/fix_issue_5

Add ContentType listing in Admin. Update documentation. Fixes #5
Remove container column from sample_example csv
Merge pull request #24 from inodb/rm_container_column

Remove container column from sample_example csv
Add Sample UID search and filter on collaborators
Merge pull request #25 from inodb/add_sample_search_filter

Add Sample UID search and filter on collaborators
change concentration units and add a unit for salinity
Merge remote-tracking branch 'bills/master' into fix_issue_26_add_SagPlateDilution
updating this branch with the bills/master
Correcting the error shown when trying to add a new SAG plate dilution.
This error was shown because the class SAGPlateDilution doesn't have any extracted_cell attribute
group_id_keyword='sag_plate__extracted_cell__sample__id' istead of group_id_keyword='extracted_cell__sample__id'