Code and View updates for sites/index.php

This work is in preparation for asking sites to update their PCU information for Monitor.

I've created a better view for sites/index.php. It lists all nodes and allows techs or PIs to associate nodes with a PCU.

Additionally, the organization of the code is split more clearly between a template (standard html with minimal php variables, and loops) and control function.

I believe this will make it easier to integrate with additional ajax code later. I will request OneLab for comments on the code reorganization, using sites/index.php as an example.