Added homophily ratio in basic schelling example

[vbv-shm]

Changed homophily comparing logic as per discussion in #2515.
Now homophily_ratio is checked for agents to be happy. homophily_ratio is similar neighboring agents divided by the total number of neighbors.

[EwoutH]

Thanks for the PR! Could you update your PR description to contain all the necessary information to understand this change on its own? You can use this template if you want.

Edit: I saw there's also this PR open, which also modifies schelling:

• Fix: Schelling Model Neighbor Similarity Calculation #2518

Are there any conflicts between them? I would tend to let #2518 go first, since it was opened earlier. (or did we assign someone to this specific issue?)

[vbv-shm]

@EwoutH Thank you for the reply.
I have understood that #2815 will be given priority because it was opened first. Still, can I work on this PR just in case #2815 doesn't work out? Or is this PR required to be closed?
From now on, I will be careful not to open PR for some issue if PR is already opened.

[quaquel]

I have provided feedback in #2518, if that is not addressed in the coming days and there is no further response, I am fine with merging this instead.