[CF-metadata] Some new standard names for cloud feedback study

[Jonathan Gregory]

Dear Tomoo

As you and I have already discussed, I think this approach and these names are
fine. The units of a quantity with name tendency_of_X are 1/s * the units of
the quantity X. In the names you have so far proposed, X has units kg m-2
e.g. cloud liquid water content, so the new quantities are in kg m-2 s-1.

Best wishes

Jonathan