Simple policy reasons for instance specific policies

Closes #1850 (closed)

• Deprectate strings for SimplePolicy
  • Give warning when strings detected
  • When strings detected, rewrite config
• All mrfSimple should work with tuples and not with strings any more (strings have been rewritten during the deprecation test, see previous point)
• Same for quarentine settings
  • Deprecate and rewrite settings with strings
  • Make it work with tuples instead of strings
• Same for transparency_exclusions
  • Deprecate and rewrite settings with strings
  • Make it work with tuples instead of strings
• Change in the docs (at the very least the cheatsheet, but check for other occurrences as well) and changelog
  • SimplePolicy
  • quarentine
  • transparency_exclusions
• Write DB migrations (see old branch priv/repo/migrations/20200913125549_simple_policy_string_to_tuple.exs)
  • SimplePolicy
  • quarentine
  • transparency_exclusions
• change config/description.exs so all changed settings use tuples
  • SimplePolicy
  • quarentine
  • transparency_exclusions
• Change what nodeinfo returns without breaking backwards compatibility
  • SimplePolicy
  • quarentine

MR's for FE's

• Pleroma-fe should be ready to be merged when this MR is merged
  • MR to admin-fe: admin-fe!187 (merged)
• Admin-fe is ready but still needs review
  • MR to pleroma-fe: pleroma-fe!1263 (merged)