Rudimentary support for VersionOne.
Adding working VersionOne implementation.  Fixes #149.
Collect the OID, too, just in case it might be needed for future API operations.
Add story number and priority fields.
Follow the same pattern as the redmine importer for what to name the project name configuration option.
Adding documentation for new VersionOnes service.
Assemble keyring URL in get_keyring_service method; allow blank passwords to be entered.
There's no reason for this to be a set rather than just a normal tuple.
Merge pull request #150 from coddingtonbear/add_version_one

Add support for importing Tasks from VersionOne