Smartspace - Listen for SHOW_NOTIFICATIONS setting

If enabled, do not show any smartspace content besides weather, for
both the current user and the managed profile. This should match
existing notification behavior on the lockscreen.

Fixes: 220881135
Test: atest LockscreenSmartspaceControllerTest

Change-Id: I8c542a3a3c5d53ee39a2d1565651e3cd21b0744e