Stuck in a tornado

This is the first release of MAVCesium bringing with it quite a few changes from the prior codebase:

• Sockets and static files are now served by a single Tornado server
• The module can now be reloaded in MAVProxy
• Cesium version update
• Application prefixes are now supported with/mavcesium being the default
• Experimental support for displaying sensor footprints on terrain
• UI update to bootstrap 4
• Added the ability to run MAVCesium stand alone from MAVProxy