JBIDE-13987 : introduce Proxy Wizards

Proxy Wizards are loaded from the remote discovery url and cached locally,
for offline use. Stale cache discoveries are purged after each successful
update.
If a wizard is not actually installed, say the OpenShift Application one,
we open the installation wizard to install all the required OpenShift IUs

Signed-off-by: Fred Bricon <fbricon@gmail.com>