Failed Download Handling

Re-opening the pull request on the development branch.

Old request: #329

Details:

Currently, it functions like this:
Disable "Post-Process Only Verified Jobs" in SABnzbd.
SABnzbd tells us when a download fails--no need for user intervention if we sent it the nzb.
On the manual post processing page, there's a checkbox to mark a manually downloaded nzb as bad.

I haven't tested it with any other nzb downloaders, and there's no way for a user to mark an auto-selected nzb as bad, since there shouldn't be a need to (with SABnzbd, at least).

I can make any changes you want to make this work how you think it should.