Search: Show total sum of matched transaction

[mtotschnig]

Currently when the list is ungrouped, the list header shows the sum of the matched transactions. If the list is grouped, each group shows the sum for the group. User suggests to add the total sum over all groups to the UI. One option could be that it replaces the current balance shown in the action bar, but this would be difficult to achieve technically, since the information in the action bar is populated from the account cursor, and not from the transaction list.