Implement CSV importer for agency data

Give admin ability to import a large number of agencies at a time, using spreadsheet that includes agency address, contacts, etc. along with what kinds of food they can accept. 
*accepted food types are in the form of 0's and 1's, per each food type id determined by Feeding America. 

https://github.com/HayleyCAnderson/SaferNYC/blob/master/app/models/mode_marker.rb