Merge tag '2.10.9'

* tag '2.10.9': (25 commits)
  version bump to 2.10.9 + changelog
  set immutable flags for backup notifications
  skip empty uris on attach
  pulled translations from transifex
  do not retrieve media attributes from encrypted files
  make launch conversation and launch tor pending intents immutable
  pulled translations from transifex
  pulled translations from transifex
  do not accept empty credentials as ice-restart
  add immutable flag to pending alarm intents
  add migration tutorial
  Fix typo
  try to detect if a container contains video or audio
  request bluetooth connect permission
  add permission checks to appRTCBluetoothManager
  bump targetSdk to 32
  ignore race condition after reject from notification
  use threemas webrtc build (trial)
  upgrade okhttp
  remove null bytes from strings before creating sql statements in backup
  ...

add migration tutorial

* Create migrating_to_new_device.md

* Add link to Readme for further information.

* Added some info

* Make separate backup guide and integrate Readme information with new guides.

Co-authored-by: Licaon_Kter <licaon-kter@users.noreply.github.com>

remove docs folder

* mission statement is now hosted on https://gultsch.de
* XEPs.md has been replaced by conversations.doap
* observations.md is just outdated and boring by now

Merge branch 'master' of github.com:siacs/Conversations

fixed markup in observations.md

Merge branch 'master' of github.com:siacs/Conversations

Merge pull request #2230 from AnBuKu/patch-1

Added XEP-0384

Added XEP-0384

Maybe style [XEP-0384: OMEMO Encryption](http://xmpp.org/extensions/xep-0384.html) would be better for user's convenience; of course for other XEP's as well

add support for XEP-0377: Spam Reporting

add xep-0084 to docs/xep.md. wikipedia was complaining about it missing

add some missing XEPs to docs

opt-in to send last userinteraction in presence

updated XEP list

Merge branch 'development' of github.com:siacs/Conversations into development

Merge pull request #1000 from kriztan/patch-4

added XEP-0085: Chat State Notifications to docs

Update XEPs.md

added XEP-0085: Chat State Notifications

Merge branch 'development' of github.com:siacs/Conversations into development

Merge pull request #992 from kriztan/patch-4

added XEP-0092: Software Version to XEPs.md

added XEP-0092: Software Version to XEPs.md

Merge pull request #866 from SamWhited/xep0245

Add XEP-0245 (/me command) support