Configurable minimum/maximum delegation limits

[przemyslaw]

The validator should be able to configure minimum and maximum delegation amounts to manage the delegator set more efficiently.

*configurable per Validator

• min / max parameter (number of tokens)
• should not be possible to be higher than network maximum
• allows to control dust

This in effect means that if a validator sets a delegation limit and some delegator stakes are outside the limit, those delegators will be automatically unstaked (following a normal undelegation flow with a delay) before the next auction is run.

[wojcik91]

initial analysis notes: https://tnt.sh/s/9e81ef15-9ed9-4a8f-8db7-edafb2ae4505