adding stats option for remote query

[paolap]

I'm adding the stats option for remote so one can get a summary of what has been published.
This is already working in new branch remotestats.
I only needed to retrieve the attributes from the dataset ids .
It works for both CMIP5 and CMIP6, but CMIP5 doesn't return variables in the ids.
The CMIP5 issue should be resolved for other parts of the code see #105

[paolap]

This is done as of release 0.7