Fix infinite event listener ping-pong destroying settings page

[Kuuuube]

Regression introduced in #1270 (ecd9ffc).

The newly introduced 'element' type for dom data binder to update things which are not any type of input (checkboxes, text inputs, etc) can cause an infinite loop when updating the value.

There is a potential ping-pong between

yomitan/ext/js/dom/dom-data-binder.js

Lines 149 to 168 in ecd9ffc

	_applyValues(targets, response, ignoreStale) {
	for (let i = 0, ii = targets.length; i < ii; ++i) {
	const [observer, task] = targets[i];
	const {error, result} = response[i];
	const stale = (task !== null && task.stale);
	if (error) {
	if (typeof this._onError === 'function') {
	this._onError(error, stale, observer.element, observer.metadata);
	}
	continue;
	}
	if (stale && !ignoreStale) { continue; }
	observer.value = result;
	observer.hasValue = true;
	this._setElementValue(observer.element, result);
	}
	}

and

yomitan/ext/js/dom/dom-data-binder.js

Lines 211 to 216 in ecd9ffc

	_onObserverChildrenUpdated(element, observer) {
	if (!observer.hasValue) {
	return;
	}
	this._setElementValue(element, observer.value);
	}

When the value is updated by one of them, the other triggers, updating it again, triggering the other, and so on. This can occur any time the dictionary aliases in the settings page are updated, including when it is initially loaded.

I've added a guard against 'element' being updated by _onObserverChildrenUpdated. The 'element' type can be expected to have special handling in all cases and should not need to use this.

I've also reverted the styling change that was applied to _onObserverChildrenUpdated in the dictionary aliases pr to make calling this._setElementValue(element, observer.value); appear as a more explicit action instead of a default action.

Tested on Firefox and Chromium.