handleSaveApply(ev, mode) {
			return this.handleSave(ev).then(() => {
				classes.ui.changes.apply(mode == '0');
			});
		}
The handleSaveApply function is invoked when the user clicks
the `Save & Apply` button in the page action footer.

The default implementation should be sufficient for most
views using {@link form#Map form.Map()} based forms - it
will first invoke
{@link LuCI.view.handleSave view.handleSave()} and then
call {@link ui#changes#apply ui.changes.apply()} to start the
modal config apply and page reload flow.

Views not using `Map` instances or requiring other special
logic should overwrite `handleSaveApply()` with a custom
implementation.

To disable the `Save & Apply` page footer button, views
extending this base class should overwrite the
`handleSaveApply` function with `null`.

The invocation of this function is wrapped by
`Promise.resolve()` so it may return Promises if needed.

@instance
@memberof LuCI.view
@param {Event} ev
The DOM event that triggered the function.

@returns {*|Promise<*>}
Any return values of this function are discarded, but
passed through `Promise.resolve()` to ensure that any
returned promise runs to completion before the button
is re-enabled.