Implement check for fixtures version

[Antrikshgwal]

What was wrong?

download_fixtures method doesn't check for fixture version and re-downloads fixtures even when the same version already exists on the location.

Related to Issue #728

How was it fixed?

Implemented a mechanism that stores the URL while downloading fixtures and compares it with the URL used on subsequent function calls. Since the URL changes on a version change, we can know if the version has been changed and if we need to re-download the fixtures. Otherwise, we can skip the download.

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[SamWilsn]

In 8f3ffd3f0d I updated the fixture fetcher to cache downloaded files. Do you think the optimization you have here is still worth it, and if so, would you be interested in rebasing it or should I?

[Antrikshgwal]

In 8f3ffd3f0d I updated the fixture fetcher to cache downloaded files. Do you think the optimization you have here is still worth it, and if so, would you be interested in rebasing it or should I?

I think 8f3ffd3f0d is a more robust approach while still optimising the fixture fetching. So, it would be a better option.