Move context event handler code into separate
WorkbenchPartReference method to ensure that "getClass()" and "this"
refer to that outer class, not to the anonymous EventHandler class.

Change-Id: Ieb2c2b42703e38920e652556aeb1d08e38565a7f
Signed-off-by: drgler <daniel.kruegler@gmail.com>
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>