Remove the unused buildings model
Add form_picker_controller test, and prevent invalid downloads
Add the pdftk gem

This should let us cut out the dependency on the pdftk web service, and not have
to make a bunch of web requests all the time.
The download test passes again, and FormPickerController produces @resident
Revert "Add the pdftk gem"

This reverts commit 8ec5a3d00f1acc22cedc28d0c1c29f6cbd96a653.

Wrong gem for pdftk.  What I wanted was pdf-forms.
Fill forms locally with pdf-forms

This gets rid of the dependencies on GSA-OCSIT/pdf-filler, saving us from
relying on web requests to, and the existence of, an outside-hosted web service
and PDF forms.  The app is now self-contained, and you can fill/download the
sample forms with no internet connection at all.

The two sample forms are in /public/forms.  The database seeds and test
fixtures are generated from those.
Update the README for the pdf-forms gem