Add query variable to the filename for downloads

[evoloshchuk]

Problem

When one downloads the result of a query that has variables, the filename does not indicate which values were used. This is confusing when it has to be done for multiple values of the variables (no way to distinguish which saved file belong to what combination of variables).

Solution

This parch includes query variables and their values into the filename.

Example

Given A query named "example-query" with 2 variables "a" and "b" has been run with a=1 and b=2. Actual The filename, when downloaded, is example-query.csv. Proposed The filename, when downloaded, is example-query-a-1-b-2.csv

[pedrocarmona]

@ankane is it possible to merge to master?

[rpmadalena]

Have the same issue, @ankane any plans to merge this?

[mshytikov]

Any chance that this could be merged ?