Use Neomodel instead of py2neo. [FEEDBACK WANTED]

[Askir]

This is how Neomodel would work.

But in general I think the library is quite a bit better. It also has the ability to have Models for Relationships so we are able to save properties in the "TAGGED_WITH" Relationship for example. Which is really nice imo and was definitely missing in py2neo.

The interface isn't perfect. For some reason the interal neo id is exposed as .id which is really annoying because now we have to use id_ again to save our own uuid. But at least they provide an easy property for that yay!

Some other things that made me stumble:

• The uuid is saved as hex (without the hypens "-") but when exported via Marshmallow the hypens are added again... So the returned id cannot be searched for in the database. you have to remove the hyphens first.
• All find or all methods we used before are via the interface object.nodes.xyz which again doesn't hide the graph very well. But I think we can provide our own wrappers for that again if we want to.
• In general the interace is more adapted to django than rails so I am not quite as familar with it but I guess @arne-z is going to like it.

[Askir]

Pipeline broke I know it's just a spike PR so everyone can see how it would look like. I didn't delete all references to py2neo yet sorry.

[Askir]

@erksch would there be any problems in the frontend if from now on we would ommit the hyphens in uuids?

[Askir]

E2E is fixed with this PR in Jona: https://github.com/hpi-sam/ask-your-repository-web/pull/42 just waiting for eriks approval.

I know this is a huge PR again but I'd really appreciate reviews at least on a basic level. To make sure everybody understands what this was about and also to make sure I didn't miss any obvious problems

[erksch]

@Askir There would be now problem whatsoever in the frontend. If the ID is consistent in all resources everything will work

[erksch]

@Askir Great work overall! Well tested imo.