Filter changes browsing by ACL

Signed-off-by: Michal Čihař <michal@cihar.com>
Avoid explicit ordering of Change objects

This is already the default one.

Signed-off-by: Michal Čihař <michal@cihar.com>
Provide centralized ACL filtering for Changes

Signed-off-by: Michal Čihař <michal@cihar.com>
Use centralized last changes filtering

Signed-off-by: Michal Čihař <michal@cihar.com>