HAMT-72: Refactor Community Vault - PurchaseTracker Relationship

[jrkosinski]

Changes

NOTE: Merge LoadPipe/hamza-escrow#14 first

Refactoring:

1. CommunityVault is responsible for distributing rewards, and keeping track of how much was distributed to each address.
2. CommunityRewardsCalculator is used by CommunityVault, and is responsible for calculating how much to distribute to each recipient
3. PurchaseTracker is used by PaymentEscrow to record activity, and is used by CommunityRewardsCalculator to determine (according to some strategy, which is CommunityRewardsCalculator's responsibility) how much each recipient should get.
4. CommunityVault holds a reference to CommunityRewardsCalculator
5. CommunityVault holds a reference to PurchaseTracker
6. PurchaseTracker no longer holds a reference to CommunityVault
7. Change out CommunityVault's CRC to change the strategy by which rewards are calculated.
8. Modified Deployment script to deploy a CommunityRewardsCalculator

Tests:

1. Removed some tests from PurchaseTracker, and moved those tests to CommunityVault
2. Added tests in CommunityVault
3. Revised tests in CommunityVault to match new structure