Marge bot integration

[David Hurka]

> AFAIR each MR was handled one at a time. Having said that, Marge also
> has a batch mode that will batch together multiple MR's and will test
> and merge them together.

This sounds sensible to me.

GitLab merge trains have the idea to merge everything on a temporary branch, 
and then test each merge commit individually. All successfull ones are then 
applied to master.

But I wonder whether testing each single merge commit is necessary. I think it 
is uncommon that one MR breaks something and the next one fixes exactly that, 
or even that only a combination of 2 MRs, but not 3 MRs has a problem. Most 
automatic tests are probably not good enough to find all such problems anyway.

So, batching together and testing together seems sensible. Also in terms of 
ressource usage, which I think is worth mentioning. :)

(I do not have lots of experience with such stuff.)