Automatically generate database queries

[jalextowle]

PR #793 introduced a large change to Mesh that completely overhauled the database layer. In the file db/sql_implementation.go, several handwritten queries were created. These queries could create maintenance issues down the road, and it would ultimately be safer to use a different solution to generate these queries.

One solution to this problem would be to use an ORM of some kind to automagically generate the queries.