ledger: Add fund ledger report type.

See the FundLedgerODS docstring for details.

ledger: Dedicated reporting tab for Expenses:Payroll.

To better accommodate the new payroll-type metadata.

ledger: Add Equity back to default project report sheets.

While many projects often won't have anything here, this is necessary to
show project funds released from restrictions.

ledger: Formatting modernizations.

* Equity sheet(s) report project.
* Headers include account classification.
* Bottom lines are formatted in the usual accounting way.

cliutil: Add ReturnFlag.

Take this opportunity to re-standardize flag values now that it's clear
what's most common.

ledger: Add transaction-level reports.

Mainly for the cash disbursements and receipts reports, which have dedicated
shortcuts.

ledger: Only display accounts requested with --account.

Now that we're accepting classifications, it's possible to specify account
options that select some but not all accounts at the same level of the
hierarchy. This commit tracks requested account names separately from sheet
names to do that correctly.

ledger: --account accepts a classification.

This makes it easier for users to specify a group of accounts.

ledger: Include all fund accounts in default project ledger reports.

This brings the reporting into sync with the fund report.

ledger: Correct period totals. RT#11661.

The period totals were reporting the balance of all the loaded postings, not
just the ones in the reporting date range.

Like the accrual report, introduce a RelatedPostings subclass that records
and saves all the information we need at group definition time, to help us
get it consistently right rather than redoing the same math over and over.