Create whitelist addresses for delegation

[przemyslaw]

This will enable the validator to split his delegators into two groups:

• generic group (as we see it now)
• whitelisted group.

Each group will have different staking rewards fees. The whitelisted group will have a limit on the number of delegators to make sure that the Validator can offer these slots to its customers.

An enhancement would be to allow different fee groups/packages for different delegators:
Basic: 1% but no support for the average user
Advanced: 3% but phone support, analytics etc.

Right now max 1200 delegations

• should be a system contract not a functionality of the node

• teonite will do a analysis on system possibilities
• consider forceful migration