Clean up dust delegations / forced undelegation

[przemyslaw]

t should be a configurable option - what is dust for the validator? Then, for instance, if less than 100 CSPR are sitting for more than three months without any change, undelegate it.

The catch with this is "dust" means what? Big accounts can leave big dust. So, it can be tricky not to have this happen. Some large accounts are 2k+ CSPR per era. So, the formula might need

x% of undelegate amount left or < 500 CSPR, which is greater. Or if the amount left is equal to the last rewards +/- certain percent, then call dust.

Forced undelegation - whether the validator should be allowed to trigger the undelegation process. The dust config option could be used here on the generic level. There could also be a targeted undelegation option.

Adding limits and undelegating those below or above the limits solves this task.

[wojcik91]

Forced undelegation of stakes below/above specified delegation limits has been implemented as part of #4.

Does that fulfill this requirement?