Rename repo from onlineanalysis to MENTO

The name 'onlineanalysis' is too generic to refer to the python modules in the repo.

I already used 'MENTO' (= Maxwell-Enhanced Near-real-Time Online analysis) to describe this package for SRI 2021, I think we should change the name of the repo here on Gitlab too.

Additionally, I would change the name of the package itself, which is a breaking change for current users. AFAIK only P10 and P11 use it currently. I can change the client code for P10. For P11, I think the existing client code in CrystalControl (the P11 control SW) actually just copy-pasted functions directly without importing the modules, so it should also not affect them.