Every time someone tries to use it, it goes mad and tries to scrape the
entire fediverse for no visible reason, it's better to just remove it
than continue shipping it in it's current state.

idea acked by lain and feld on irc

Closes #1595 #1422

- [] for options
- <> for mandatory arguments
- foo ... when foo can be repeated

[ci skip]

Closes: https://git.pleroma.social/pleroma/pleroma/issues/1621

[ci skip]

Needs to be backported to stable.

Related: https://git.pleroma.social/pleroma/pleroma-support/issues/29

A warning was added, but their were some newlines and whitespaces missing which broke the rendering of the setting. I've added them now

Related: https://git.pleroma.social/pleroma/pleroma/issues/1594

I also made a more explicit distinction between OTP and from source installs in the general explanation

I added a new file to explain
* where a custom theme can be created
* where themes can be downloaded
* where to add the theme on the server
* how to make the theme available on the instance
* how to set the theme as default on the instance

Closes: https://git.pleroma.social/pleroma/pleroma/issues/1164

* Added "Migrate" to the title because these steps can also be used to migrate the instance to another server
* Added an optional step to reinstall pleroma (esp. for migrating servers)
* Currently the steps threw an error 'could not execute query: ERROR: function "activity_visibility already exists with the same argument types'
   * I added a new step to drop and recreate an empty pleroma-database
   * I played around with the `-c` and `-C` options of pg_restore, but dropping and recreating seemd to be the only way I got it working
   * This was tested on Debian Stretch, psql (PostgreSQL) 9.6.15

Large part of it was no longer true (i.e none of the changes need
recompilation anymore and you can't brick an instance by changing them,
it's not necessary to manually truncate the db manually anymore)

Our nginx config will happily pass `Forwarded`/`X-Real-IP` from the
client. Caddy, Apache and Varnish pass `X-Forwarded-For` as well anyway.

Closes: https://git.pleroma.social/pleroma/pleroma/issues/1061

* Put url's between angle brackets. docs-develop doesn't list the url's as links, I assume these will fix that (but don't know if I can check)
* Added a third space before the "sub"bulletpoints. docs-develop doesn't show them as subpoints with only two spaces. I hope three will fix it (but don't know if I can check)
* Added a newline above the bulletpoints because otherwise they are broken on docs-develop
* Remove the :smile: thingies because neither of the docs (docs.pleroma.social and docs-develop.social) show them as emojis
* Add a link to fediverse.network
* Update to add new stuff and fix things that aren't correct (any more)