Clear cache completely on delete()

In case a ClassName is existing twice, the previous approach fails.
I encountered this problem with an imcomplete module installation. Repeated installation resulted in multiple tabs added, but the uninstall only found the first tab to uninstall - after that getIdFromClassName() returns a wrong result.
Merge pull request #1745 from M-Mommsen/patch-1

[-] BO : Clear Tabs cache completely on tab deletion