Add battery_warning config JSON file.

res/(battery_warning.wav, battery_warning/(warning.wav, config.json))
	-Add resource dir for `battery_warning.py`.
	-Add configuration file, `config.json`, and move
	`res/battery_warning.wav` to `res/battery_warning/warning.wav`.

shell_scripts/battery_warningd.py
	-Add `load_config()`, to load configuration variables from
	`res/battery_warning/config.json`; replaces the global settings
	constants (eg `BATTERY_CHECK_INTERVAL`, `UPPER_LEVELS`).
Remove use of logging from battery_warningd.py.

shell_scripts/battery_warningd.py
	-Remove use of the `logging` module, which was used primarily
	when debugging the script's occasionally defunct audio (fixed in
	cfd8c30).
Merge branch 'feature/battery_warning_refactor' into develop

res/battery_warning/config.json, shell_scripts/battery_warningd.py
	-Move `battery_warningd.py` configuration variables to a
	configuration JSON file, `config.json`.