Format photo exposure time as rational when applicable

Summary:
If value is below 0.3, format the output as
rational which is commonly used in photography.
Value is computed from the double input value.

CCBUG: 343273

Reviewers: bruns, ngraham

Reviewed By: bruns

Subscribers: kde-frameworks-devel, Baloo

Tags: Frameworks, Baloo

Differential Revision: https://phabricator.kde.org/D21533