[dolphin/search] Reset search options when needed

Summary:
Adds a method to reset the options in `facetsWidget` in two cases: when disabled and before parsing a new search URL.
Otherwise, controls for a parameter (ex. `rating`) which are not found in the new URL would stay on the old positions, instead of the default "any".
See D24422

Test Plan: Controls on `facetsWidget` go back to the default in such two cases.

Reviewers: #dolphin, elvisangelaccio, meven, ngraham

Reviewed By: ngraham

Subscribers: kfm-devel

Tags: #dolphin

Differential Revision: https://phabricator.kde.org/D24450