[Symfony] additional form types

[kbond]

Currently, the only form types available are the Pending{File|Image}Type's. These mimic the core FileType behavior exactly. I think this is fine but we could probably add some additional ones.

Some ideas:

• FileType: saves a PendingFile to a File on a specific filesystem (probably temporary) - will need path generation.
• ImageType: saves a PendingImage to an Image on a specific filesystem (probably temporary) - will need path generation and maybe manipulations?
• A compound type that includes one of the types above with delete/view/download options. Perhaps these should be native options to the above types?