Download history database

[rgathub]

Description

This PR adds option to enable a sqlite database for all downloads using hash to avoid downloading the same file again.
It also fixes the latest oAuth issue with latest version of PRAW.

Changes

• Fixes oAuth issue with latest version of oAuth.
• Adds flags "enable_downloads_db" and "downloads_db_name" to create a sqlite database that stores records of downloaded files to avoid duplicate downloads in future.
• Removed gyfcat as it does not exists from tests.
• Updated test resources as some no longer exists or have updated hashes.

Existing Issues

• Imgur support is out dated and is not working.