shell: List all interesting network interfaces

... except the interface being configured, when configuring children or
parents.

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Refactor common parts of bond and bridge settings

Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Arrange slave interface checkboxes vertically

Fixes #841
Reviewed-by: Stef Walter <stefw@redhat.com>
shell: Use a drop-down for network bond primaries

Fixes #844
Reviewed-by: Stef Walter <stefw@redhat.com>
shell, NM model: Use symbolic names for the DeviceType property

Closes #1040
Reviewed-by: Stef Walter <stefw@redhat.com>