Implement git repository for config changes

[JonathanShaw]

Initial work on making jvmctl use a local git repository to store changes to config files for #20. Tries to label commits sanely and attribute them to the user running the command. This change adds a dependancy on git, though this was pretty much a soft dependancy already.

Adds two new commands to jvmctl whose names I'm not completely sold on suggestions welcome

• changed --shows the most recent commit that matches the nodes name.
• revert -- reverts the most recent commit that matches the nodes name

One flaw is that if a node's name is a subset of another node (say banjo and banjo-testing-foo) then the changed and revert commands aren't going to work as intended, Maybe change the commit message to wrap node.name in something that cant be part of the name?

[ato]

One flaw is that if a node's name is a subset of another node (say banjo and banjo-testing-foo) then the changed and revert commands aren't going to work as intended

Could you 'git log banjo.conf' rather the next 'git log --grep banjo'?

[ato]

Nice work!

[JonathanShaw]

Those changes are included now.