Merge pull request #30 from MargaretLangley/master

spec create displays form errors
commiting refactored due_ons spec and fixes before removing unneeded tests.
due_ons removed specs for moving between due_dates and per_month  due_ons
createEntities uses the polymorphic description in the migrate create_entities
refactored charge_row_spec
Fix charge_row.empty? adds day: 0, month -1
Merge pull request #32 from MargaretLangley/master

Payments not validated for zero amount
Texts for invoices held in csv files, sheet & sheet_address,  and created in a rake task