wip - background upload session
working background session / manager

this is a bit overly optimistic...it assumes that once the upload task has been created
and the temporary file has been written that it will *eventually* get to the server

the in-memory store is then purged of the cached data.

this is not very fault-tolerant...but want to try something.
updating uploader status message
notes
changing task dictionary file extension

NSDictionary saves the file as a plist. this just makes it easier to inspect the file.
adding batch uuid string to request via NSURLProtocol class method

this permits later retrieval in the delegate methods to aid clean-up.
also, implementing a Background Task to ensure that the file deletion and
task dictionary clean-up steps are completed.
setting static string for batch id key
updating background session manager

present notifications for the completion of each task, success or failure.
use Caches directory for temporary files rather than tmp dir
cleaning up outdated comments
bumping version number to reflect background url session addition
increasing min iOS version to 7.0 for background url session
Merge branch 'feature/background-upload' into develop