Get One Income Source's Year Setup

How one income source is reporting the year: the accounting basis, the periods of account and the late accounting date rule election, with who last set each from Sodium. Periods of account and the late accounting date rule are self-employment only; supportsPeriodsOfAccount and supportsLateAccountingDateRule say whether they apply at all, so 'does not apply' is never mistaken for 'nothing declared yet'.