Merge branch 'use-transactional-db-api' into 'master'

...-api/src/main/java/org/briarproject/bramble/api/Pair.java

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

...main/java/org/briarproject/bramble/api/db/DbCallable.java

...main/java/org/briarproject/bramble/api/db/DbRunnable.java

...ava/org/briarproject/bramble/client/ClientHelperImpl.java

...briarproject/bramble/contact/ContactExchangeTaskImpl.java

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

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

...rg/briarproject/bramble/identity/IdentityManagerImpl.java

.../briarproject/bramble/lifecycle/LifecycleManagerImpl.java

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

...rg/briarproject/bramble/settings/SettingsManagerImpl.java

.../org/briarproject/bramble/sync/DuplexOutgoingSession.java

...n/java/org/briarproject/bramble/sync/IncomingSession.java

...org/briarproject/bramble/sync/SimplexOutgoingSession.java

.../org/briarproject/bramble/sync/ValidationManagerImpl.java

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

...iarproject/bramble/transport/TransportKeyManagerImpl.java

...oject/bramble/versioning/ClientVersioningManagerImpl.java

...org/briarproject/bramble/client/ClientHelperImplTest.java