Bug 521484 - Async content-assist can freeze UI Thread

Added async proposal filtering to avoid defaulting to sync proposal
retrieval

Change-Id: Ibdc3767359e7fe6f4ff8d52d8cd895e1ddea04ae
Signed-off-by: Lucas Bullen <lbullen@redhat.com>
Also-By: Mickael Istria <mistria@redhat.com>
6 files changed