Revised trace substance sensors

Added default value C_start=0. Added documentation to example. Added sensor with two ports to examples
Revised sensors.

Renamed Examples.ExtraProperties to Examples.TraceSubstances
Removed commented line.
Corrected class name
Changed model name of trace substance source.
Added package.order, removed upper limit for loop, and removed dash in sed which is not supported on OS X.
Renamed source to TraceSubstancesFlowSource
Renamed source to TraceSubstancesFlowSource
Moved initial equation section
Put all parameters and all public classes into the same section
Removed commented code
Removed unrequired public statement
Restructured code
Revised code
Revised html
Added new time series to reference results