feat(discord)!: beef up discord integration

[wass3r]

❤ THANKS FOR HELPING OUT :D

Proposed change

fixes #121 and then some..

BREAKING CHANGE:
This change will break existing Discord bots only as it introduces a new mandatory config variable discord_server_id. That means, one bot per server, which is true for Slack bots already as well.

In addition to addressing the referenced issue, this PR adds:

• treating roles as user groups
• ability to use allow/ignore rules
• can use direct_message_only
• can use output_to_rooms
• can use output_to_users
• and more...

Tested the above (but maybe missed some things).

Planning to make some addendum to the docs to cover server id and permission scopes for bots

Types of changes

What types of changes is this pull request introducing to flottbot? Put an x in the boxes that apply

• Bugfix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist

You can fill this out after creating your PR. Put an x in the boxes that apply

• I have added tests that prove my fix is effective or that my feature works
• I have added necessary documentation (if appropriate)

[coveralls]

Pull Request Test Coverage Report for Build 267

• 27 of 170 (15.88%) changed or added relevant lines in 7 files are covered.
• 10 unchanged lines in 4 files lost coverage.
• Overall coverage decreased (-1.3%) to 38.48%

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Changes Missing Coverage	Covered Lines	Changed/Added Lines	%
remote/slack/remote.go	0	1	0.0%
remote/slack/helper.go	0	2	0.0%
utils/access_check.go	13	22	59.09%
remote/discord/util.go	0	11	0.0%
remote/discord/remote.go	0	57	0.0%
remote/discord/helper.go	0	63	0.0%

Files with Coverage Reduction	New Missed Lines	%
remote/discord/helper.go	1	0%
remote/discord/util.go	1	0%
remote/discord/remote.go	4	0%
utils/access_check.go	4	69.23%

Totals
Change from base Build 264:	-1.3%
Covered Lines:	820
Relevant Lines:	2131

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💛 - Coveralls