DarkMode Tile affects all users + security bug

When setNightModeActivated is called, the change affects the current logged in user
Also, permission checks are made before changing dark theme
Test: manual
Bug: 168039904
Merged-In: I7786d9dde10f7547f5dd9fb00661fb89fde9f05c
Change-Id: I7786d9dde10f7547f5dd9fb00661fb89fde9f05c
(cherry picked from commit f16e87a9)