A basic implementation of a CSV dump for crops
added dates created/modified to crops csv
rails g scaffold Harvest...
Added associations between harvests, crops, and members
set cancan abilities for harvests
Prettified harvest form

Also renamed "notes" to "description" in database
Prettified all the harvest views
Validate units (must be one of individual/bunches/kg/lb)

Also changed "units" attribute to "unit". Oops, we weren't following the
Rails naming convention.
Validate quantity/unit for harvests

If quantity is blank, we also set unit to blank.
Added friendly urls to harvests
improve display of quantities
added harvest link to signed-in homepage
Merge pull request #322 from Skud/harvests

Harvests
Separated informal/human units from measured weights
Merge commit '24255411c9d5907ebb6e8fcb39b6bca1833559d9' into csv
Tweaked crop CSV to include added_by and license
Added harvest CSV
If quantity == 0, set it to nil
allow per-owner CSV downloads
added links to CSV and JSON data