company: Add new fields to the company info form

Previously, new fields would never show up on the company info page
forms: Clearing answers cache should be null

The check in DynamicFormEntry::getAnswers() will use the cached _values
array if it is not set to null. Previously, the ::save() method would set it
to an empty array.
Merge pull request #273 from greezybacon/issue/company-info-new-fields

Auto add new fields to the company information form

Reviewed-By: Peter Rotich <peter@osticket.com>