Do not hide sharing URL automatically

Summary:
When sharing screenshots on Imgur, Spectacle hid the resulting URL after
a timeout, with no way to get it back.

It's more userfriendly to require explicit closing of the inline message
in that case.

Depends on D13247

Test Plan:
Export → Share → Imgur should not hide inline message
automatically anymore.

Reviewers: Spectacle, ngraham

Reviewed By: Spectacle, ngraham

Differential Revision: https://phabricator.kde.org/D13261