Add status entry for showing scheduled transactions in ledger view

This is useful to see if any scheduled transaction has not been entered
especially in the case that the 'Display schedule transactions with planned
post date' is switched on.

Cherry-picked from commit 2502a10da/review D16911 and adjusted to branch 5.0.

BUG:401079
FIXED-IN:4.8.3,5.0.3
Reviewed By: tbaumgart
Differential Revision: https://phabricator.kde.org/D16916