Add target (seems strange) to trigger while waiting for better trigger templating

Blueprints are severely limited because of the llimited templating support for triggers.
I propose in the interim that we add a “target” attribute to the following trigger platforms:

* state
* template
   If provided, in addition to the template, look for entity_id's  here.
Maybe others:
* tags
* ???

With the limitation that any templates used in the target setup, are only evaluated at configuration time.

Use Case:
Exisitng blueprint example: “Motion Activated Lights” triggered by multiple motion sensors.