Show alias for introduction notices in private conversation

...ava/org/briarproject/bramble/api/identity/AuthorInfo.java

...iarproject/briar/android/contact/ConversationVisitor.java

...arproject/briar/api/introduction/IntroductionRequest.java

...rproject/briar/api/introduction/IntroductionResponse.java

...iarproject/briar/introduction/AbstractProtocolEngine.java

...rproject/briar/introduction/IntroduceeProtocolEngine.java

...arproject/briar/introduction/IntroductionManagerImpl.java

...t/briar/headless/messaging/MessagingControllerImplTest.kt