Don't skip certain recent documents in kicker and taskmanager

Summary:
Due to KRecentDocument::add() bug, application name '<app>' could
be stored for recent documents instead of its desktop entry name
'org.kde.<app>'. This issue mostly affects items opened from apps
themselves, while items opened from e.g. Dolphin are not affected.
(The bug is fixed by D10863, but we depend on Frameworks 5.42 which
doesn't include it.)

Kicker and taskmanager used to query for '<app>' agent only, thus
excluding items with correct 'org.kde.<app>' agent.

This commit makes kicker and taskmanager query for both '<app>' and
'org.kde.<app>' agents in order to get all recent documents for the
application.

Test Plan:
  # Create 'test1' and 'test2' text files.
  # Open 'test1' in Kate from Dolphin.
  # Open 'test2' from Kate itself.
  # Right-click Kate in Kicker/Kickoff and Task Manager and check
    that both files are present there.

Reviewers: #plasma, broulik, hein

Reviewed By: #plasma, hein

Subscribers: anthonyfieroni, ngraham, plasma-devel

Tags: #plasma

Differential Revision: https://phabricator.kde.org/D10890