Case insensitivity in Twitter screen names can be a headache

[reefdog]

Twitter considers slifty and SLIFTY to be the same, as they should, as they are identically insufferable. But our pipeline would consider them different, mostly because we store the screen names as-is and Postgres treats each variation uniquely (as it should).

While it'd be good to continue storing the screen names as entered by the user or as they canonically are in Twitter (often their casing makes them more readable), it would be nice if we were also storing a lower-case transformation for performing unique constraints (and being able to essentially do case-insensitive searches).