Add Valve, PRV, Reactor, Disinfection, and Separation classes

[fletchapin]

Is your feature request related to a problem? Please describe.
There are some PyPES classes not currently supported by the GUI.

Describe the solution you'd like
Add the Valve, PRV, Reactor, Disinfection, and Separation classes to the PyPES GUI.

Describe alternatives you've considered
Currently, a user would have to programmatically edit their model with custom Python code or manually edit the JSON file. Both are quite tedious.