[bramble] Add support for contact aliases

...in/java/org/briarproject/bramble/api/contact/Contact.java

.../org/briarproject/bramble/api/contact/ContactManager.java

...va/org/briarproject/bramble/api/db/DatabaseComponent.java

.../org/briarproject/bramble/contact/ContactManagerImpl.java

...e/src/main/java/org/briarproject/bramble/db/Database.java

...va/org/briarproject/bramble/db/DatabaseComponentImpl.java

...c/main/java/org/briarproject/bramble/db/JdbcDatabase.java

...main/java/org/briarproject/bramble/db/Migration40_41.java

.../briarproject/bramble/contact/ContactManagerImplTest.java

...rg/briarproject/bramble/db/DatabaseComponentImplTest.java

...st/java/org/briarproject/bramble/db/JdbcDatabaseTest.java

...riarproject/bramble/identity/IdentityManagerImplTest.java

.../bramble/properties/TransportPropertyManagerImplTest.java

...st/java/org/briarproject/bramble/test/DbExpectations.java

...a/org/briarproject/bramble/test/RunTransactionAction.java

...rg/briarproject/bramble/transport/KeyManagerImplTest.java

...t/bramble/versioning/ClientVersioningManagerImplTest.java

...java/org/briarproject/briar/blog/BlogManagerImplTest.java

...r/privategroup/invitation/AbstractProtocolEngineTest.java

...ivategroup/invitation/GroupInvitationManagerImplTest.java