This PR attempts to fix #3

As armv7 has a 32-bit limit, our current default migration datetime would quickly overflow causing error doing a gpodder2go init.

This fix changes the migration format to a sequential one, starting with 000001.

I had originally preferred to switch to a Unix Timestamp so that we can still keep some time data in the migration filename, but that would still impose a limit of 2147483647 (or Tuesday, January 19, 2038 3:14:07 AM GMT) for 32-bit devices.

Even though I would expect that 32-bit devices should have been phased out by then, it would still be irresponsible to drop support for other users still using this software on older devices then.

Important Notice

For existing users who had previously already migrated with the old timestamp, it is recommended that you force your migration as soon as you can

migrate -path=migrations/ -database sqlite3://${DB} force 000001