Support more than 30/31 members in a room

Created by: lerouxb

This broke when we changed the API to only return 100 max or 30 default users per page. A recent fix added pagination support to that API call, but the client doesn't use it yet.

Proposal

Whenever a message comes in, we can add that user to the member list

Relevant code,

• https://gitlab.com/gitlab-org/gitter/irc-bridge/blob/1e752b692b5ec8c64b046cccfe35d53c6e7b50bf/lib/gitter-adapter.js#L179
• https://gitlab.com/gitlab-org/gitter/irc-bridge/blob/1e752b692b5ec8c64b046cccfe35d53c6e7b50bf/lib/gitter-adapter.js#L342-356