Metadata: Add qcodes version, git status, git diff and things

There are a few points we should save for the metadata:

For qcodes

• Save qcodes version
• Save current git hash
• Save current git branch
• Save git diff if there are changes in the branch (this should be limited to not go crazy on data, notebooks in branches...)

Then there it should be encouraged that a user has all working scripts and stuff in a git repo, and for that one we should save the same information
station.add_repo('./scripts')

Then there is the situation where qcodes is a package and installed on a system without git, we need to cover that too, I guess only saving qcodes version then it ok.

I'm not a git genius, which is why it didn't come with the metadata.
How should we do this exactly?

~/g/Qcodes git:feature/pyqtgraph_improvements ❯❯❯ git describe --all --dirty --long
heads/feature/pyqtgraph_improvements-0-gb269d73-dirty

~/g/Qcodes git:feature/pyqtgraph_improvements ❯❯❯ git rev-parse  HEAD
b0485b7c5e8448ac5107a43ff05eb730114c284c

~/g/Qcodes git:feature/pyqtgraph_improvements ❯❯❯ git rev-parse --abbrev-ref HEAD
feature/pyqtgraph_improvements