Add string formatting function to property info

Summary:
Adds the ability to format the metadata value
for displaying purposes individually for each
property. Currently, users of KFileMetaData
must implement their own custom formatting
functions.
All custom formatting functions from
Baloo-Widgets and Dolphin are copied into
KFileMetaData. This can be extended later.

This adds a dependency on KCoreAddons to
KFileMetaData.

FEATURE: 398581

Test Plan: tests pass

Reviewers: broulik, bruns, mgallien, Frameworks

Reviewed By: bruns

Subscribers: ngraham, kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D17245