Double entry accounting milestone 3

[chongfun]

Implement Milestone 3 of the Rental Domain and Double-Entry Accounting Architecture.

At the end of this milestone:

RentTerm
    │
    ▼
Charge(kind: rent)
    │
    ▼
JournalEntry
    ├── Dr Tenant Receivable
    └── Cr Rental Income

and:

Charge(kind: late_fee)
    │
    ▼
JournalEntry
    ├── Dr Tenant Receivable
    └── Cr Late Fee Income

and:

Expense
    │
    ▼
Charge(kind: reimbursement)
    │
    ▼
JournalEntry
    ├── Dr Tenant Receivable
    └── Cr Reimbursement Income

must all work through the accounting foundation established in Milestone 2.

ScheduledRent and TenantCharge must be removed.

Tenancy balance must become:

sum(
  Tenant Receivable postings
  for this tenancy
  through the requested accounting date
)

rather than a reconstruction from domain tables.