* MM-147753: Verifies that users are allowed to be members of a team or a channel, based on group constraints, prior to allowing the API to add them.
* MM-14753: Allow methods to return meaningful results for deleted teams or channels.
* MM-14753: Renames methods to differentiate from permissions and other team and channel restrictions.
* MM-14753: Only check if users are team/channel members if team/channel is group constrained.
* MM-14753: Updates test function names.
* MM-14753: Changes a few method signatures.
* MM-14753: Small refactor and adds missing returns.
* MM-14753: Changes method names from Get* to Filter* name prefixes.
* MM-14753: Renames error variables.
* MM-14753: Updates method names for consistency with join table names.
* MM-14753: Adds case for non AppError return.
* Update i18n/en.json