Telemetry scheduler

Allow periods to be set to zero since it is easier than changing the updatemode.
Allow hiding of objects not present on hw.
Only apply and save metaobjects which were actually changed.
Several misc fixes. 
Doxygen would be nice to know what htis method is meant to do when the item changed.
Method name isn't very descriptive (I know this is really just a result of previous method
not already being documented)