Improve VAV heirarchy

[connorjcantrell]

• Rename "RVAV" to "Reheat VAV"
• Introduce "Cooling Only VAV"
• Introduce "Fan Powered VAV"
• Consider adding "Terminal Unit" to the end of all VAV classes.
  • VAV, or Variable Air Volume, should be understood as an attribute describing a system's capacity to adjust air volume output, not as a specific system itself. In the HVAC industry, it's more accurate to use "Terminal Unit" for systems or equipment without downstream systems. For clarity, systems with variable air volume features should be termed "VAV Terminal Unit" or "Fan Powered VAV Terminal Unit" for fan-powered versions, thus avoiding confusion and clearly distinguishing their functions.
• Move all classes mentioned above under the "VAV" (ideally renamed to VAV Terminal Unit) parent class