2nd iteration on read only channel designs

Description

add changes discussed in our design session. notes in invision:
https://projects.invisionapp.com/share/KYUBY9C96MN#/screens

QA Test Steps

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Mana

4

Assignee

Michael Gamble

QA Assignee

None

Reporter

Dennis Kittrell

Epic Link

Fix versions

None

Mattermost Team

Enterprise

Sprint

Labels

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QA Testing Areas

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GitHub Issue

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Components

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