Make repository clone directory configurable.

Configuration is stored in `config/environments/common/repositories.yml`
and supports both absolute and relative (to project root) paths.
Remove Square-specific config file
Abstract background job strategy from implementation; allow possibility of other types of backgrounding
Support for usernames with periods in the URL. Fixes #43
registration can be disabled

- add Squash::Configuration.authentication.registration_enabled
- add simple test for the registration disabled case
Flip boolean to prevent method missing errors
added missing 'registration_enabled' value when using password auth
Merge pull request #63 from TobiasRaeder/master

Added missing 'registration_enabled' when generating password based authentication.yml
Fix load issue with background runners
Update gems for new Rails VULNs
Add missing licenses