Fix memory leaks in Kexi
Summary:
Fix memory leak in AlterTableTester
Remove memory leaks in GlobalSearchTest
Fix memory leak in KexiMenuWidgetAction
Fix memory leak in Json Trader: delete plugin loaders that are skipped, delete offers in part/widget managers
(the same fix as recently in KDb)
Test Plan:
cd builddir; ctest
valgrind's memcheck ...
Reviewers: piggz, wicik, wkosowicz
Subscribers: Kexi-Devel-list
Projects: KEXI
Differential Revision: https://phabricator.kde.org/D916