[FIX] SlackBridge private channels

[nylen]

Closes #13186
Closes #9408
Closes #11356
Closes #11485
Closes #7539
Closes #10002

Changed groups.info deprecated endpoint to conversations.info.
Changed to the new endpoint to get the members of room conversations.members.
Removed the deprecated message event file_share.

I think we can close #12213 in favor of this one.

We have a channel in our Slack group that was breaking the SlackBridge:

[34mI20190124-18:11:10.535(0) SlackBridge ➔ Rocket.debug Adding Rocket.Chat channel from Slack CD56XXXXX 
[34mI20190124-18:11:10.766(0) SlackBridge ➔ Rocket.debug Channel not added 

This is a private channel, but its ID starts with C. This would already break the existing code if everything else worked, because the channel would be created as public in Rocket.Chat.

If that weren't enough of a problem, neither the channels.info nor the groups.info Slack API methods work with this channel:

curl 'https://slack.com/api/channels.info?token=xoxb-etc&channel=CD56XXXXX'
{"ok":false,"error":"method_not_supported_for_channel_type"}

curl 'https://slack.com/api/groups.info?token=xoxb-etc&channel=CD56XXXXX'
{"ok":false,"error":"channel_not_found"}

What does work is conversations.info. This doesn't have the channel.members key though, so we can get that with a separate call to conversations.members.

All other data elements needed by this area of the code are present in the conversations.info response as expected.

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[MarcosSpessatto]

According to the documentation about this endpoint, when the "limit" parameter is not provided, the default limit is 100 items. How are you dealing with it, if the channel has more than 100 members?

[nylen]

@MarcosSpessatto this is a good point. It looks like the previous limitation was 1500 members rather than 100 members:

The documentation at https://api.slack.com/methods/conversations.members does not state a hard limit, but recommends using a page size of 200. A for loop using the limit and cursor parameters should be sufficient to make this work for any number of members.

[nylen]

@MarcosSpessatto I do not have a test installation that would be appropriate to resolve this, and it's unlikely that I'll have time to look at it further. Please feel free to update this PR.

[vwbusguy]

Oddly enough, I'm able to replicate this bug. I have a private channel in Slack with a channel ID that starts with "C" and the sync silently fails between Slack and Rocket. I thought it was a failure of Private channels in general, but it does seem specific to channels with IDs that happen to start with "C".