Add H2 support and use it instead of SQLite for Bukkit

[TheE]

Support for H2 should be added at a core level once #29 is implemented.

On Bukkit H2 should replace SQLite entirely to get rid of the legacy SQLite driver dependency that Bukkit enforces (witch makes transactions impossible and blocks Flyway at 3.0). The configuration syntax will need to be updated to properly handle H2 in embedded, as well as in server mode. Import commands will need to be expanded to H2 while maintaining SQLite support.

Addresses #30.