Feature request: Offline election prediction with custom parameters

[michalisFr]

As suggested by @kianenigma, this is a request to provide functionality similar to this old offline election script.

Basically what we need is a way to predict with high probability of accuracy the election results with custom parameters. More specifically:

1. Accurately predict the next active set with the custom parameters
2. Provide reasonable nominations distribution
3. Allow for customisation of candidates. It should allow for candidates that have no bonded amount and might not even exist on-chain (i.e. dummy accounts).
4. Allow for customisation of voters with custom bonded funds
5. Allow for customisation of the active set size
6. Export the results in the JSON file
7. Export the predicted minimum and average stake
8. Wishlist: Expose an API for interaction and digestion of results

When run during the election window without any parameters it should accurately predict the next active set. Our most common use case though is to run it with parameters outside the election window to see if our plan of action will work. In this case, it should still provide highly confident results, as long as there aren't significant changes in actual staking conditions in the meantime (whales switching nominations, a lot of bonding/unbonding, etc.).

These are outlined in this (unpublished) RFP.

This is really needed for Decentralised Nodes, as it allows us to optimise our nominations for the program by trying different distributions and ensure all participants are in the active set. It is also crucial in order to predict how the active set may look like with the upcoming increases and plan accordingly.