Discover, select, and set lab vendor and test codes in the Lab Order command

[andhines]

As a plugin developer aiming to originate correctly-populated lab order commands to help clinicians improve safety and efficiency, I need to be able to find exact lab test order codes from the test compendium for the specific lab vendor being used, so that my plugin can complete the administrative work for the lab order. I also need to be able to detect the default lab vendor or discover, select, and set the lab vendor in the lab order command.

A complication for some lab tests will be AOE (ask on order entry questions). These can be handled in a later phase.