Add form field validation, especially Stars rating

[billdavisjr]

add some validation to fields where appropriate. Most especially the stars field and maybe date. Most fields are plain text so we don't care what they type

quotation_text = plain text - no validation except maybe length or empty
person = plain text - no validation except maybe length or empty
source = plain text - no validation except maybe length or empty
date_said = date as string - may be empty. Date Picker handles this automatically
stars_ratting = this needs validation. Can be empty. Values: 0, 0.5, 1, 1.5, 2, 2.5, 3, 3.5, 4, 4.5, 5.
is_favorite - boolean. Field should handle validation automatically