node certificate: make parent panel scrollable

node certificate: make parent panel scrollable

The `ACME` panel may be rendered out of sight (overflow) when there
are enough SANs on the upper `Certificates` panel to push it down
enough and the browser/display height is too small.

Enable the `scrollable` config for the parent certificate view panel
in the y-axis (vertical) to make ExtJS automatically add a scrollbar
if the content overflows. Avoid enabling it for the x-axis too as
that breaks reflow of the layout if the browser window gets resized.

Signed-off-by: Dominik Csapak <d.csapak@proxmox.com>
 [T: fix commit message to one from manager]
Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>