Rewrite battery-level warning script.

Mod:
	shell_scripts/(batteryWarningd.zsh -> battery_warningd.py)
		-Rewrite battery-level warning script in Python; currently
		tested and documented.

	shell_scripts/(batteryWarningInit.zsh -> battery_warning_init.zsh)
		-Rename daemon initializer for convention.
Merge branch 'feature/battery_script' into develop

Add a new battery-level warning script, rewritten in `Python`.