Bug 569701 - Generic Editor misses collapse/expand

This change adds a generic handlers bound to various folding commands.
This handler is enabled whenever activePart adapts to
ITextOperationTarget, so it enables folding commands on most views and
editors that leverage folding.

Change-Id: I0c054a66b93a45f34497a6dd4f488f650d9de0db
Signed-off-by: Mickael Istria <mistria@redhat.com>
10 files changed