773: Auto download parameters on CONNECTED

Work in Progress.  TODO:

- [x] Check !is_flying before sending parameter-get request (Parameters.java:154)
- [x] Start progress bar in parameters automatically
- [ ] Window leaks when leaving parameters page.
- [x] Make sure only one parameters download can happen at one time
- [ ] fix parameters download auto-restarting
Yes, it works.  Check out line 25 of this to understand why:

https://github.com/diydrones/ardupilot/blob/bea5c8ae0ce13c0ec703fbf3461951e68c3fa6e2/ArduPlane/GCS_Mavlink.pde