Bug 440289 - Combo Box in Editor 'Controls' inconsistent

- Changed combobox stylebit from SWT.SIMPLE (not useful on windows) to
SWT.DROP_DOWN
- use of JFace class AutoCompleteField instead of plugin class
Autocomplete
 
Change-Id: Ifd0e2502b02fa960197b6063504e795b04db7f8e
Signed-off-by: Fabian Miehe <fabian.miehe@cassidian.com>