Display metadata information in case only basic indexing is enabled

Summary:
Metadata was only extracted manually when the indexing was disabled
completely. In case of basic indexing, also no metadata is available,
hence also extract it then.

Test Plan:
Enable basic file indexing only (and make sure to delete old database)
Metadata for files is shown in Information Panel/Tooltips

Reviewers: bruns, ngraham

Reviewed By: bruns, ngraham

Subscribers: #baloo

Tags: #baloo

Differential Revision: https://phabricator.kde.org/D20412