[balooctl] Factor out file index status collection from output

Summary:
The three output formats (singleline, multiline, json) each implement
the collection of the file status individually.

Reviewers: Baloo, Frameworks, ngraham, astippich, poboiko

Reviewed By: Baloo, ngraham

Subscribers: kde-frameworks-devel

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D20617