And a lot more. Fleshed out some services.

This isn't really part of what link manipulation has to do. parseRequest is more or less
a helper function that should get the current request's Url and pass it to parseLink, which
then will do most of the actual work. This makes the service more reusable.

This is the same concept as the fillpdf_file_context table in D7. It
lets the module
store generation info for generated PDFs so that private storage access
checking
can work properly. I'll be simplifying this a lot in D8 and simply
storing a
URL that I can parse to get the entities whose access needs to be
checked. And
I might backport that to D7; it's much simpler.

The saving part is almost working. Need to get FillPDF file contexts
being saved properly. Then, I need to ensure that access
checking on the files works like I expect. I will probably have to
implement some hook or another.

Works for FillPDF forms now but not for generated PDFs.

Woohoo!

Still more old-style syntax lurking around.

This reverts commit 49e2bf05.

This reverts commit 3079cf5a.

This reverts commit bf4cef26.

This reverts commit fcfa48c0.

OK, honestly I just forgot to git add.

Gotta return the response!

I'm getting an error when I actually try to populate/download the PDF. There is probably
something wrong with the Request object I'm returning. But this is closer.