Fix 'No display of transactions in the tags view when tags are specified in a split'

Since it is currently not clear whether this change will lead
to unwanted side effects at other code locations, the new method
setConsiderCategorySplits() has been added to enable this
functionality.

BUG:412429
FIXED-IN:5.0.8
Test Plan: tested on linux with mymoneytransactionsfiltertest
Reviewed By: tbaumgart, #kmymoney
Differential Revision: https://phabricator.kde.org/D24426