[Improvement] Make vanities case insensitive

[jpawlowski]

I noticed that currently redirects require vanities to be exactly as added to the database.
It would be nice to have these handled as case insensitive instead so that marketing guys could write codes however they want (and users could ignore upper cases and simply enter lower case only words that would still work the same way).

┆Issue is synchronized with this Trello card by Unito

[ThDJRenton]

I would just add that if we make them case insensitive it reduces the security, mildly. 👍