SWT key handling on macOS

[eselmeister]

Some users have reported strange behavior regarding the range and distance selection on macOS. A test case to inspect it has been created here:

#257

As it turned out, instead of using SWT.CTRL, SWT.MOD1 shall be used instead. This has been also described here:
https://bugs.eclipse.org/bugs/show_bug.cgi?id=463130#c7

The following mappings shall be replaced:

• SWT.CTRL -> SWT.MOD1
• SWT.SHIFT -> SWT.MOD2
• SWT.ALT -> SWT.MOD3

See documentation in SWT.java.