Add format-no-controller to bluetooth module and fix it still being visible if the format string is empty

[PucklaJ]

Fixes #2163

This PR contains the following changes:

1. Adds the format-no-controller and tooltip-format-no-controller format strings that will be used if no bluetooth controller could be found.
2. Fixes the bluetooth module still being visible if the format string is empty.

The reason for why the bluetooth module was still being displayed is the return statement in the constructor of the bluetooth module:

Waybar/src/modules/bluetooth.cpp

Lines 95 to 106 in aecd807

	// NOTE: assumption made that the controller that is selcected stays unchanged
	// for duration of the module
	if (!findCurController(cur_controller_)) {
	if (config_["controller-alias"].isString()) {
	spdlog::error("findCurController() failed: no bluetooth controller found with alias '{}'",
	config_["controller-alias"].asString());
	} else {
	spdlog::error("findCurController() failed: no bluetooth controller found");
	}
	event_box_.hide();
	return;
	}

This return statement caused dp.emit() not to be called and somehow this removed the ability for the module to hide.

I also think that it makes sense to have an additional format string for the case when the system does not have a bluetooth controller. If the user still wants to hide the bluetooth module he just needs to set format-no-controller to an empty string.

[Alexays]

LGTM thanks!