Add root_software_release_url property on Hosting Subscription in order to store the requested software_release.

Add root_state_property on Hosting Subscription in order to store to which state the root instance was requested.

This reverts commit 99d1c52c.

My mistake. We used :
  dict.get("key") or "default"
instead of :
  dict.get("key", "default")

because some time dict["key"] is None.

This avoid looping on one item.

- Use Hosting Subscribtion as root
- Rename 'SoftwareInstance_getSoftwareInstanceUid' into
  'SoftwareInstance_getHostingSubscriptionUid' to have a meanful name.

string to vifib master.

Conflicts:
	slapos/grid/slapgrid.py

This reverts commit 0dedf0a5.
Vifib skin folder ordering has to be cleanly defined (priority=60 like for the
other skin folders).

There is no need to show SoftwareInstance_view.