make sure all outputs are known

at startup, if a screen id is missing from the screenpool mapping
containment::screen() will return -1 for a moment in the startup
phase even if it has a valid lastScreen

populate mappings of eventual missing stuff at screenpool ctor

make sure destroyed containments don't get assigned a view

reviewed-by: David Edmundson

CCBUG:372099
CCBUG:371858
CCBUG:371991
CCBUG:371819
CCBUG:371734