Add readVariable method to monitors.

Inquiries into the monitors, that is variables that
have a monitor attached to them, can be done on a
individual key, rather than getting the entire
lot and parsing them.
Added metaserver attribute and monitor variables.

The ability to add static attributes via metaattributes
section of configuration, along with specifying
monitors for attributes.
Fix a few small issues with updates.

Convert readVariable to const and adjust accordingly.
Adjust tests and callers of readVariable accordingly.