* moving from coffee to js

* renaming method

Suppress message-pinned notification from import;
Fix bug in _id generation for importer;

Fix an error on importing if there was a user by the same username on the server but different email

* Continue work started by patcon in #2272 for importing slack again and again without duplicates. Currently errors out. Also fixed #2532 for Slack and HipChat.

* Ignore new slack channel format

* Add ability to upsert messages on sendMessage

* Show a better error for duplicated oembed records

Improve the stability of the importers, reject invalid uploaded files when they don't contain any users, channels, or messages.

Greatly extend the import framework. Implemented the new framework into the slack import and added HipChat import, two examples of how to use the import framework