add instance specific panel

I hope this is better than !195 (closed)

Depends on: pleroma!66 (merged)

Applications:

• Announcement from instance admin
• Local rules
• Link to source codes with instance specific modifications

Example: https://pleroma.distsn.org

mentioned in merge request pleroma!61 (closed)

mentioned in merge request !195 (closed)

changed the description

added 1 commit

• f23940a1 - Update App.js

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added 14 commits

• f23940a1...b0f248c4 - 13 commits from branch pleroma:develop
• ebd8300e - slove conflict

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added 1 commit

• fe1044df - Update main.js

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mentioned in merge request pleroma!66 (merged)

changed the description

merged

mentioned in commit ea6ee2aa