New -patch stage features

- New key -entityid 'keyname' for -patch stage. Enables patching of
submodel
entity fields by making map/bsp entity pairs with same unique key index.
- New key -triggers for -patch stage. Enables replacing "trigger_"
entities
from .MAP. This requires gamecode support - trigger entities should be
able to initialize themself with no submodel, but only mins/maxs keys.