db normalization: consolidate CHECKINGACCOUNT and BILLSDEPOSITS, eliminate BUDGETSPLITTRANSACTIONS

[slodki]

All transaction's details from BILLSDEPOSITS can be stored in CHECKINGACCOUNT with TRANSDATE set to NULL. Then BUDGETSPLITTRANSACTIONS can be migrated to SPLITTRANSACTIONS.

• All existing queries to CHECKINGACCOUNT should verify TRANSDATE is not null
• All existing queries to BILLSDEPOSITS should read details from linked CHECKINGACCOUNT and SPLITTRANSACTIONS
• There is no data lose as TRANSDATE is always equal to NEXTOCCURRENCEDATE in BILLSDEPOSITS

Schema changes (BILLSDEPOSITS simplified, BUDGETSPLITTRANSACTIONS removed):

I don't know if data migration could be implemented in pure SQL...