Add option to remove manually approved certificates

OTR: Fix onContactStatusChanged & dont archive OTR

- Fix session handling on contact status change: Do not reset
  potentially active sessions; check peer's OTR-resource on disconnect
- use no-permanent-store hint instead of no-store to ensure
  finished messages are delivered to offline/disconnected clients
- add no-permanent-store to ask compliant servers not to archive
  OTR messages

when touching the border of the snackbar or more precisely the space between the input field and the snackbar Conversations would switch into a random conversation for yet unknown reasons.

- "Remove certificates" option brings up a dialog that allows
  to delete certificates from MemorizingTrustManager's keystore
- Reconnect active accounts when certificate-settings are changed
- new preference category "Certificate options"

Merge branch 'dont_trust_cas_preference' of https://github.com/BrianBlade/Conversations into BrianBlade-dont_trust_cas_preference

Conflicts:
	src/main/res/values-de/strings.xml
	src/main/res/values/strings.xml

Bugfix for issue #1121

check with lowercase to also match JPEG, JPeg ...

changed image url in comment

Add a new "Don't trust system CAs" preference under advanced options
that will change the behaviour of the MemorizingTrustManager. All
formerly unknown certificates will raise a warning if checked.

Enable end-conversation by swipe gesture