Parameters: Use APM parameter metadata if available when editing parameters

Metadata: 
Place the ParameterMetaData.xml file from APM MissionPlanner in DroidPlanner's 'Parameters' directory for parameter display names and units while in the Parameter activity - allowed values and descriptions to come.

Settings:
Use Settings -> Advanced -> Parameter Metadata to select the vehicle type metadata to be used. [ None, ArduCopter, ArduPlane, ArduRover ]
![screenshot_2013-10-13-13-19-55](https://f.cloud.github.com/assets/4014433/1322444/49c98098-342e-11e3-8618-867dba1a7d21.png)
![screenshot_2013-10-13-13-26-17](https://f.cloud.github.com/assets/4014433/1322445/50639862-342e-11e3-8723-061735bbf669.png)