Add off-target information to downloaded files

[vineetbansal]

Allow the user to optionally download off-target information in the downloaded csv/json files. Also remove support for excel files.

[1rzhu]

The off-target-included csv result is available for download in PR #47 , by adding a new data format in job_query.result.

There is still an issue that needs our attention - the Off-target position and Off-target region-string are inconsistent due to the 0/1-indexing problem.