Visual treatment for subtransactions that don't match total

[scottohara]

When creating a split transaction, we allow the transaction to be saved even if the sum of the subtransactions don't match the total for the parent split.

(So that we can save a 'partial' transaction and return later to correct).

In the transactions index, we should show some sort of visual indicator/warning for these, so it is clear that there may be a problem with the transaction.