Git-me-the-url

Remove dependency on deprecated pkg_resources

Suppress nag message from gitpython if git is not installed.

Fix incorrect GitLab URL

Fix typos

**Changes**
* Rewrote implementation of translators to make defining a URL generator for a new service much easier.
* Add caching to improve performance of repeat queries

Changes:
* Remove clipboard option
* Ignore origin/HEAD when searching for branch name
* Fix plugin loading for non-cli usage