Use compact Json format when converting query URLs

Summary:
There is no need for indenting (less data to transfer over
the local socket, but no functional difference), and it makes
the 'baloosearch' window title in dolphin somewhat readable
again (no more URL encoded newlines, less spaces).

Test Plan: dolphin baloosearch:

Reviewers: Baloo, Frameworks, ngraham, astippich, poboiko

Reviewed By: astippich

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D20345