Destroy removal visuals after idler

Destroy removal visuals after idler

There was some bug when visual destructor called during
it's emit ResourceReady.

To avoid this case, Let we keep visuals more long term,
and Discard + Destroy after some idler called.

To avoid multiple Idler callback register,
let we make that idler callback in VisualFactory.

Change-Id: Id47083b158f91bb81666d6f2100811dedb0d70f1
Signed-off-by: Eunki, Hong <eunkiki.hong@samsung.com>