Recurring transactions

Have a way to configure recurring transactions.

Features of a recurring transactions:
- account
- isTransfer
 - sourceAccount
- description
- amount
- start date
- end date (optional)
- frequency (inspired by GCal, as flexible)
- action [automatic, ask first] (inspired by http://www.turtlesoft.com/Goldenseal-Software-Reference/recurring.htm)

Issues:
Since wxBanker isn't necessarily going to be running constantly, when run, it needs to look at its list of recurring transactions and figure out which transactions to make. What is the best way to remember this state? Checking for all transactions which "should" exist won't work since it should be possible to remove or edit recurred transactions, and we don't want wxBanker to re-enter these.

Something like GCals editing would be optimal where, when editing or removing one transaction, you can choose to apply it to just this instance, all future, or all past and future. In order to do this, transaction metadata linking to the recurring transaction would be necessary.

However a still decent option would be to record with each recurring transaction setting, the last time the transaction was entered. Then when wxBanker is run, it can look at the last date the recurring transaction was made, and make all appropriate ones from then to the present.