InputPanel: fix column scaling behavior

InputPanel: fix column scaling behavior

When scaling the browsers content either via the browser itself or
because the OS has a different scaling / DPI setting, it can happen that
not all columns have enough space next to each other and thus the last
column is moved further below.

This happens especially on chromium bases browsers (e.g. chrome, edge).

Changing the layout to use extjs HBOXes with flex instead of columns
solves works well.

Signed-off-by: Aaron Lauterer <a.lauterer@proxmox.com>