Currently Eclipse processes key bindings from "disabled" activities,
activity support for key bindings was broken during e4 transition in
2010.

This change re-implements activity support for keybindings
contributions.

- Don't show filtered key bindings in Keys preference page
- Hide bindings for filtered keys to BindingTableManager
- Fail command execution for filtered activity
- Update bindings state if enabled activities change

Fixes https://github.com/eclipse-platform/eclipse.platform.ui/issues/2859