[tx] Support opening and migrating V1 SQL schema stores

[ncalexan]

For simplicity, #170 supports only creating a fresh V2 SQL schema store (and, I suppose, opening it again).

This ticket tracks doing the little bit of work to migrate a V1 SQL schema store forward to V2.

[rnewman]

Notably one needs to:

• Bump part range:

https://github.com/mozilla/mentat/blob/master/src/common/datomish/sqlite_schema.cljc#L158

• Transact the new data:

https://github.com/mozilla/mentat/blob/master/src/common/datomish/db_factory.cljc#L84

[rnewman]

Concur on closing this as WONTFIX, @ncalexan? Let's just ship 0.1 with its own starting schema version.

[ncalexan]

Sure, that's certainly less work :)