RocketChat 2.4.1 issues

[ShellyXueHan]

Is your feature request related to a problem? Please describe.

This is to track all the issues found from the test RC instance with version 2.4.1:

• iOS login Error Code -1200 still exists
• market place apps not enabled, account needed
• incoming webhook has invalid image url

[filiy]

@filiy to look at marketplace apps issue

[ShellyXueHan]

incoming webhook example issue tracked here: https://github.com/RocketChat/Rocket.Chat/issues/15494