Add support for opening or printing of multiple reports

In the report overview select multiple reports and select one of the
available entries in the context menu opened with right mouse click.

Cherry-picked from branch 4.8, commit bf6278f9.
Adjusted for KF5 by Thomas Baumgart.

BUG:401080
FIXED-IN:4.8.3, 5.0.3
Reviewed By: tbaumgart
Differential Revision: https://phabricator.kde.org/D17231