Form Parser improvements for date, datetime & choice form types (format & types)

Adds `date`, `datetime` & `choice` format support.
For `date` & `datetime` fields it is a date format.
For `choice` it is a list of values formatted as a JSON string.

Partially covers https://github.com/nelmio/NelmioApiDocBundle/pull/297 (date format & add support of collection)