impl PoS inflation system

[tzemanovic]

This is the master set of issues for implementing the PoS inflation and rewards systems.

Designed as specified in:

• Clarify inflation system calculation details #230
• PoS spec updates #283
• Update inflation spec #613
• PoS spec fixes #788

Currently, almost all of the code is in #388, but the plan is to separate this down into smaller PRs.

Individual items and issues (checked if completely addressed so far in #388 or in another PR):

• PoS - unbonding should update validator stake and voting power at pipeline offset #366
• PoS rewards based on voting info #353
• Phase out use of VotingPower struct #455
• Update PoS parameter values #478
• Implement reward products #499
• Replace f64 with rust_decimal in token conversions #436
• Updates in block signing stake are delayed from tendermint #642
• Remove validator staking reward address #498
• Validator commission rates #695
• PoS add re-delegation #34
• Refactor Validator Sets #721
• Refactor ValidatorState #787
• Implement cubic slashing #892
• Fractional amounts of tokens when applying rewards products and slashes at withdrawals #805
• Apply inflationary rewards to voting power #939

Latest details on state of progress:

• Current PoS development is largely based on PoS: lazy map epoched data #740, which changes the PoS code to rely on lazy data structures for storage reading+writing.
• PoS: lazy map epoched data #740 currently needs fix iter prefix #913 to be completed in order to properly test the changes. PoS - unbonding should update validator stake and voting power at pipeline offset #366 is included in PoS: lazy map epoched data #740.
• PoS inflation and rewards #714 is the initial implementation of the inflation and rewards system. This PR includes PoS rewards based on voting info #353, Implement reward products #499, and Updates in block signing stake are delayed from tendermint #642 from above. Would probably like to get this merged and finish remaining PoS tasks in new PRs on top of this to prevent it from getting too large. Also probably still needs to be changed a bit once rebased onto a complete PoS: lazy map epoched data #740.
• Implement cubic slashing #892 currently relies on PoS: lazy map epoched data #740 and will partially address Refactor ValidatorState #787.
• Refactor Validator Sets #721 will be mostly developed after PoS: lazy map epoched data #740 and PoS inflation and rewards #714 are ready as a base and will address most of Refactor ValidatorState #787.
• PoS add re-delegation #34 and Apply inflationary rewards to voting power #939 will likely be developed once PoS: lazy map epoched data #740 and PoS inflation and rewards #714 are ready as a base.

[brentstone]

Closing this now that #2006 exists. The only remaining items in here are redelegation and the final PoS rewards.