Include base database name in created databases

[symroe]

I suspect this is more or less the same use case as #20 but slightly different.

If I have a database foo set up in DSLR and I run dslr snapshot bar the created database name is something like dslr_123456_bar, where 123456 is a timestamp.

I have more than one project set up on my dev machine and I tie the snapshot names to Git branch names.

If I'm working on a feature that spans more than one project I might make branch names that are the same.

Of course I can mitigate this by running dslr snapshot [project_name]_bar, but it would be useful if generate_snapshot_db_name would add dbname.