[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