infopanel fully resizable

Summary:
Currently Infopanel does wrap its title when trying to narrow it.
Initially:
{F5619283}
Expanded:
{F5619284}
Resizing fails, watch cursor:
{F5619286}
Patch applied:
{F5619287}

Maybe this behaviour it intentional. Personally, I prefer the patch.

Test Plan:
compile & run
Resize infopanel with long title

Reviewers: #dolphin, ngraham, elvisangelaccio

Reviewed By: #dolphin, ngraham, elvisangelaccio

Subscribers: renatoo, vhanda, nicolasfella, elvisangelaccio, ngraham

Tags: #dolphin, #kde_applications

Differential Revision: https://phabricator.kde.org/D9664