Deprecate MySQL support

[dennissiemensma]

It seems that MySQL has too many issues with DST. Also, the new DB-features of Django in #72 lack decent support.

I think I'll have to deprecate it, and support an management command as well to easily migrate all data to PostgreSQL.

[dennissiemensma]

I'm not sure about this yet, but it will make support a lot easier as well. TODO for later.

[dennissiemensma]

Now I'm pretty sure.

It's causing too many issues and I can't guarantee decent timezone support. Also, adding a field to a table rebuilds the entire table, which PostgreSQL does not require (when default value of new field is NULL).

Upgrading a 1-year instance of dsmrreader from v1.4 to v1.5 took 20+ minutes. And because MySQL does not support schema migrations in transactions, the migration will break as well when anything happens.

[dennissiemensma]

Well, I rewrote quite some docs and placed warnings regarding MySQL.

I also completed a migration script to copy data to PostgreSQL using Django. It's quite slow, but I do not see another reliable way of migrating data without users having to debug stuff themselves.

I'll also insert a notification for any MySQL users pointing at the migration docs.

[dennissiemensma]

Merged doc changes back to 1.6 branch. Migration script should be part of #223.