Fix timeout errors

[raclim]

Progress towards #3096

Changes:

• Removes optional callback from findByEmailOrUsername() from server/models/user.js and temporarily ignoring the case sensitivity option that determines which database call to return, since where it's currently being used doesn't seem to have any major effects for now. This definitely needs to be revisited, but just seeing if this will temporarily mitigate the current issue for now.
• Adds try/catch blocks and more error handling for copying objects from s3 in server/controllers/aws.controller.js and for sending mail in server/utils/mail.js

I have verified that this pull request:

• has no linting errors (npm run lint)
• has no test errors (npm run test)
• is from a uniquely-named feature branch and is up to date with the develop branch.
• is descriptively named and links to an issue number, i.e. Fixes #123

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