Add handshake key pairs to DB, remove inactive contacts.

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

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

...rproject/bramble/api/contact/event/ContactAddedEvent.java

.../bramble/api/contact/event/ContactStatusChangedEvent.java

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

...va/org/briarproject/bramble/api/identity/LocalAuthor.java

...va/org/briarproject/bramble/api/transport/KeyManager.java

...rc/test/java/org/briarproject/bramble/test/TestUtils.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/Migration42_43.java

...src/main/java/org/briarproject/bramble/plugin/Poller.java

...ject/bramble/properties/TransportPropertyManagerImpl.java

...va/org/briarproject/bramble/transport/KeyManagerImpl.java

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

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

.../org/briarproject/bramble/db/DatabasePerformanceTest.java

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