Fix the error handling in the db module

[tcharding]

I have started this work already, adding issue to fit my work flow in with the team process and also to help keep me in scope. This is a pre-issue ticket for an issue already in this sprint, pulling this one straight into the sprint. There will be more Sqlite issues to come.

#1243

The database module got merged with messy error handling as a result of Tobin's inexperience. This needs cleaning up

Tasks

• Add custom Error to db (Sqlite)
• Have a single error variant in metadata_store that holds the Sqlite Error
• Define custom error variants for all error cases in db and embed errors in them i.e., don't use Io(String use instead Io(io::Error)