Add rewards staking / voting for validators

[punkrock]

The main reason for people to use Lisk Mobile or Lisk Desktop is to send tokens and get rewards. Therefore I highly recommend to add this feature. Users should be able to search for validators and vote for them. As simple as possible. Just a list of validators sorted from "high rewards" to "low rewards", the amount field where I add the LSK I want to lock on the chosen validator and an info about how many LSK I get as rewards if I vote for the validator.

[ManuGowda]

Thank you @punkrock for the suggestions, we are inching closer to production and at this stage we are freezing the feature implementation.

All the features that was reviewed by our auditor is what we aim to release for major release now, however we can consider these requirements for next minor releases.