Update for pyam 07

[Rlamboll]

Pull request

Please confirm that this pull request has done the following:

• Tests added
• Documentation added (where applicable)
• Example added (either to an existing notebook or as a new notebook, where applicable)
• Description in CHANGELOG.rst added

Adding to CHANGELOG.rst

Please add a single line in the changelog notes similar to one of the following:

- (`#XX <https://github.com/GranthamImperial/silicone/pull/XX>`_) Added feature which does something
- (`#XX <https://github.com/GranthamImperial/silicone/pull/XX>`_) Fixed bug identified in (`#YY <https://github.com/GranthamImperial/silicone/issues/YY>`_)

[Rlamboll]

Since the new version of pyam is buggy, unless anyone objects this update will be written so as to be backwards-compatible rather than removing deprecated .scenarios() etc. commands.

[znicholls]

Couple of tweaks but otherwise all good