tmf: Fix various leaks in Histogram

tmf: Fix various leaks in Histogram

Fix Image and Color leaks in Histogram class. Also fix Font leak in
HistogramTextControl. HistogramTextControl's derived classes were
overriding dispose without calling super but those were not necessary to
begin with.

Bug: 428491
Change-Id: I23a9b85a26f00b809a1748e886202a5de07cd35e
Signed-off-by: Marc-Andre Laperle <marc-andre.laperle@ericsson.com>
Reviewed-on: https://git.eclipse.org/r/22696
Tested-by: Hudson CI
Reviewed-by: Bernd Hufmann <bernd.hufmann@ericsson.com>
IP-Clean: Bernd Hufmann <bernd.hufmann@ericsson.com>
Tested-by: Bernd Hufmann <bernd.hufmann@ericsson.com>