gui/cluster: add CorosyncLinkEdit component to support up to 8 links

gui/cluster: add CorosyncLinkEdit component to support up to 8 links

CorosyncLinkEdit is a Panel that contains between one and 8
CorosyncLinkSelectors. These can be added or removed with according
buttons.

Values submitted to the API are calculated by each
ProxmoxNetworkSelector itself. This works because ExtJS searches
recursively through all child components for ones with a value to be
submitted, i.e. the CorosyncLinkEdit and CorosyncLinkSelector components
are not part of data submission at all.

Change ClusterEdit.js to use the new component for cluster join and
create. To make space in layout, move 'password' field to the side
(where the network-selector previously was) and use 'hbox' panel for
horizontal layouting to avoid spacing issues with languages where the
fieldLabel doesn't fit on one line.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>