1268: Roundcube db r=Nebukadneza a=micw
## What type of PR?
feature
## What does this PR do?
- makes roundcube work with mysql
- runs db init/upgrade scripts on startup
- redirects roundcube logs to stdout
### Related issue(s)
- preparations to solve #1226
- closes#1157 (side effect ;-) )
## Prerequistes
- [x] Unless it's docs or a minor change: add [changelog](https://mailu.io/master/contributors/guide.html#changelog) entry file.
Co-authored-by: Michael Wyraz <michael@wyraz.de>
Co-authored-by: micw <michael@wyraz.de>
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