Cleanup DB init()

[ross-spencer]

GenerateBaselineDB is returning a database connector which means it is creating an empty database regardless of whether we then call GenerateBaselineDB.dbsetup() which is where this could/should(?) happen. Impact should be minimal while this isn't fixed - the file-handle will be overwritten, e.g. in unit tests. It would be good to clear this up when there is an opportunity.

[ross-spencer]

Language-wise, if we break compatibility then perhaps users will be more familiar with:

1. initialize db class and metadata.
2. call get_database().

So we'd change dbsetup to get_database which removes any confusion between initialization and then getting a database connector.