Suggested new Equipment Classes

[Steve Appling]

I would like to suggest three new Equipment Classes that I have needed and which seem generally useful.  I will create a pull request with these, but thought I would bring up the topic here first to see if there was any feedback.

• brick:Chilled_Water_Bypass_Valve    - A valve installed in a bypass line of a chilled water loop
• brick:Chilled_Water_Isolation_Valve  - An isolation valve installed in the chilled water loop
• brick:Plate_Heat_Exchanger - A heat exchanger that transfers heat between two separate fluids through thin metal plates.

There are existing classes for Condenser Water Bypass and Isolation valves, but not for Chilled water.