User AS: details, create, edit

[matzf]

Create a Form: prompting for:

• attachment point
• label (optional)
• VM?
• VPN? (if available on the selected attachment point?)
• if not VPN:
  • IP
  • NAT: internal IP, internal port (optional)
• port

Create a View to create a new user AS using this form. On submit, this will:

• generate/assign an AS-identifier
• generate keys and certificates for this AS
• create an AS object in the DB with:
  • ISD set to the ISD of the attachment point
  • exactly one Host object, with IP=localhost
  • one Service object for each of the "normal" AS services (ZK, BS, CS, PS)
  • a Link to the attachment point
  • VPN, if configured
• (later: trigger updates for attachment point)
• redirect to the AS detail page

Create a View to see the details of and edit an existing AS, using this form. On submit, this will:

• update certificates if attachment point changed to different ISD
• update the properties (as above)
• redirect to the same page

Not part of this issue: trigger configuration update for attachment point