Allow other database drivers

[barryvdh]

I can understand the preference for sqlite, but if you want to allow other database, this should be relatively easy

• the foreign key is created before the database. Not sure why it works in sqlite, but mysql fails
• The themes.sql is only for sqlite. I changed it to a command to export to a php array, and used the regular import. Should give the same effect and maybe just as easy to export/edit?