Marking some code that isn't compatible with Mono

The equality (==) operator between types (Type class) is not supported
in Mono.
Added a measurement structure
Implemented most (if not all) of metric history

* The metric history class can record measurements.
* Values can be estimated between measurements.
* A limited number of measurements are kept (currently 360, may increase
this later).
Implemented properties and methods

Uses Linq and existing functionality from underlying MetricHistory
class.