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
A kudos for Kevin!
https://github.com/diydrones/ardupilot/commit/240a9ccaf098fe53c3da2fb93507ba4070ff9b6a
https://github.com/diydrones/ardupilot/commit/996eda0080f76be25e37b2c06efd4d02fa20082a