Make Yakuake work on Wayland with Qt 5.9

Summary:
Yakuake is also affected by the common problem that the integration
breaks once a window gets hidden, which is a very common feature of
Yakuake.

This change tracks the PlasmaShellSurface, destroys it on hide and
recreates on show. Thus it's alwyas positioned as expected.

Test Plan:
This commit was created using a yakuake which is positioned
correctly, although I pressed F12 a few times.

Differential Revision: https://phabricator.kde.org/D7709