impl PoS inflation system

[tzemanovic]

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

Designed as specified in:

• #230
• #283
• #613

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):

• [ ] #366
• [ ] #353
• [x] #455
• [x] #478
• [ ] #499
• [x] #436
• [ ] #642
• [x] #498
• [x] #695
• [ ] #34
• [ ] #721
• [ ] #787