Added rake task to import new crops from CSV
Load multiple crop CSV files from seeds.rb

We factored out a Crop.create_from_csv method to avoid duplicated code.

Note: naming convention with db/seeds/crop*.csv is to use a 2-digit
number for ordering.  00 and 10 chosen (with a gap in between) because I
learned to program in BASIC and it seemed like a good idea just in case.
Added some comments/docs to Crop.create_from_csv
Merge pull request #328 from Skud/crop-csv-upload

Crop csv upload