Link headers in following/followers API should include follow_id as max_id/since_id.
However, these API use current_user's account_id instead of follow_id from #3167.
This causes irrelevant result on loading more users.
* Always set `overflow: auto` to allow scroll just after opening
* Remove bounce animation which may cause unintended behavior due to max-height
* Use CSS transition instead of react-motion
* Some CSS refactoring including className changing
unarist