Use a read-only TextPropertyDescriptor for event properties

Use a read-only TextPropertyDescriptor for event properties

Use a custom, read-only TextPropertyDescriptor to use the cursor
in the value column to scroll for long property strings. In the
previous implementation, long value strings couldn't be read properly.

Change-Id: I6469442cb5b8f6779c807e90f8dc569ed3f71b49
Signed-off-by: Bernd Hufmann <bhufmann@gmail.com>
Signed-off-by: Alexandre Montplaisir <alexmonthy@voxpopuli.im>
Reviewed-on: https://git.eclipse.org/r/11984
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>