As a user, I would like the ability to suppress certain DGM references from content assist

As described in https://issuetracker.springsource.com/browse/STS-1987, certain DGM references in content assist are not used very often and can clutter the content assist operations.

There should be a preference option to hide little-used DGM references from content assist.

A grander version of this feature would allow users to select their own DGM methods to filter, but a first go at this would be to hard code a list.