[FIX] Importers not recovering when an error occurs

Improve how the importer progress gets sent to the client and change the structure of the importers imports

[FIX] Slack import failing and not being able to be restarted

[FIX] Slack import failing and not being able to be restarted
# Conflicts:
#	packages/rocketchat-i18n/i18n/en.i18n.json

[FIX] Csv importer: work with more problematic data

Interface clean up, with users&channels being allowed to be empty for
CSV import.

[FIX] Fix file upload on Slack import
# Conflicts:
#	packages/rocketchat-importer/server/classes/ImporterBase.js

Closes #7447

..whoops..

fixes #4614 : check user.profile.email and fallback with username: user.name if it does not exist in user record

* moving from coffee to js

* renaming method

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