Fix mouse wheel zoom and text control value handling in histogram view

Fix mouse wheel zoom and text control value handling in histogram view

Partial fix for bug 384423.

Add focus gained listener to child text controls of Histogram composite
that gives focus to canvas which handles mouse wheel events.

Provide the HistogramZoom instance owned by the full trace histogram as
a mouse wheel listener to the time range text control.

Update time range text control to prevent unnecessary reloading of the
time range histogram model when focus is lost without changing value.

Update current time control to prevent resetting of current event on
parsing error.

Fix possible SWT exception in histogram text control during Eclipse
shutdown.

Change-Id: Iefd4db5eafbe54e9386a9ec23b4ac1ecd2ce2a1b
Signed-off-by: Patrick Tasse <patrick.tasse@gmail.com>
Reviewed-on: https://git.eclipse.org/r/12902
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>