Release 4.1.6-rc1

• Cargo tracking will now correctly count all instances of the same type of cargo for different missions. Previously it only counted the cargo for
  the last mission requiring that cargo type, as found in Cargo.json.

• The loaded contents of Cargo.json can now be found in monitor.state['CargoJSON']. monitor.state is what is passed to plugins as state in the journal_entry() call.

• Our logging code should now cope with logging from a property.

• Miscellaneous updates to PLUGINS.md - mostly to clarify some things.