Bugfix/empty csv for manually selected files

[BrianWhitneyAI]

Description

The purpose of this pr is to resolve #415. We have a situation with imported data where the query we build to download a csv does not account for single selected files ie. (CTRL + Select) this is because we pass it a list of index ranges. which might look like:

                    indexRanges: [
                        { start: 0, end: 0 },
                        { start: 2, end: 2 },
                    ],

When we build a query it does not register these ranges since they're not inclusive. However if we pass it indexRanges: [{ start: 0, end: 2 }] it works correctly.

Changes

• Add conditional to handle single index files
• Seperate the download method which has gotten quite heavy
• Add tests for this case (Comparing the query)