[WIP] Issue 835 speech warnings

Settings have been implemented.  Now the features need to be implemented:

- [ ] Solar Activity Warning
- [ ] Wind Speed
- [x] 400ft ceiling exceeded
- [x] arming failure
- [ ] low signal strength
- [x] lost signal
- [ ] low battery
@TShapinsky you'd want to store `121.92` as a constant, using the constant name to describe what the value is used for.

I get that `121.92m == 400ft`, but for anyone not familiar with the code, the value looks meaningless, and arbitrary.