Fix Unsplash POTD not updating
Summary:
The bug only affect Unsplash POTD provider. If you choose Unsplash POTD, the wallpaper won't update daily.
Previous patch for Unsplash Wallpapers changed the identifier format, for example, unsplash:123456 is not a fixed date identifier. So we can not simply detect whether an identifier contains date by looking for :. This patch detect date string with regular expression.
Reviewers: Plasma, ngraham
Reviewed By: ngraham
Subscribers: ngraham, plasma-devel
Tags: Plasma
Differential Revision: https://phabricator.kde.org/D22925