MySQL storage implementation

[RJPercival]

We should create a MySQL-compatible storage implementation. The rootsanalyzer (PR #40) currently cannot get root certificates from the rootsgetter because we have no persistent storage implementation.

[RJPercival]

We could use GORM, the ORM, which would also support Postgres and SQLite, amongst other databases. However, it would add a layer of abstraction which might make the code harder to understand than a straightforward MySQL implementation using the database/sql package.

[Mercurrent]

It's discussable whether GORM makes it always harder to understand the code. Sometimes it makes it surprisingly easier. Worth discussing on code-examples when they come to life.

[rmhrisk]

In general, I do not like ORMs because they tend to make supportability harder and they come with performance and scalability penalties. With that said it seems that the use case here may be simple enough to make its use acceptable?