Add X-Plane Simulator Plugin
Initialize database and raise exceptions when keys don't exist

The database is initalized in the database module and reads and writes
will now raise exceptions if the key doesn't exist in the dictionary.
This should make it easier to catch errors in plugin development.
Add command line arguments to configuration that's passed to plugins
Begin work on xplane plugin
Work on X-Plane plugin sending data
Merge pull request #2 from birkelbach/master

Feature Freeze