[Done] New try at upgrading to 0.18.1 July 1st 20:00 CET

We'll give the upgrade new try tomorrow. I've had some good input from admins of other instances, which are also gonna help troubleshoot during/after the upgrade.

Also there are newer RC versions with fixed issues.

Be aware that might we need to rollback again, posts posted between the upgrade and the rollback will be lost.

We see a huge rise in new user signups (duh.. it's July 1st) which also stresses the server. Let's hope the improvements in 0.18.1 will also help with that.