v7.0.0

CHANGES:

• Do not install opam-installer in images any more. This turns
  out to be a largely optional component as the opam binary
  installer doesn't include it either. It will be made optional
  in the final opam 2.1 release. (@avsm)

• Build multiple versions of opam in the base images. This results
  in an opam-2.0 and opam-2.1 binary being installed, with
  a hardlink to opam <- opam.2.0 so the defaults are unchanged.
  This allows upstream CI images to switch the hardlink to make
  it easier to test newer releases of opam, and also upgrades.