[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 the `prefs` instance field in the `DroidPlannerPrefs` class should be used mostly if a `SharedPreferences` object is needed. 

Whereas possible, you'd want to have `DroidPlannerPrefs` provides methods to access the preferences values.
For example: `mAppPrefs.isTtsCeilingExceeded()` instead of `mAppPrefs.prefs.getBoolean("tts_ceiling_exceeded",true)`.

When retrieving the value for a preference, store the default value as a constant, and use the `preference key` via the string resource: `mAppPrefs.prefs.getBoolean(context.getString(R.string. pref_tts_warning_400ft_ceiling_exceeded_key), DEFAULT_TTS_CEILING_EXCEEDED)`.

This allows to easily change either underlying values, without needing to chase, and update all the references in the code.

You can take a look at the `DroidPlannerPrefs` class implementation to see examples of what I mentioned.