Add buffersyncer

.../justjanne/libquassel/protocol/api/dto/BufferSyncerDto.kt

...otlin/de/justjanne/libquassel/protocol/api/proxy/Proxy.kt

.../de/justjanne/libquassel/backend/BufferSyncerPersister.kt

...e/justjanne/libquassel/connection/ClientSessionHandler.kt

...t/kotlin/de/justjanne/libquassel/client/QuasselApiTest.kt

...in/de/justjanne/libquassel/persistence/AliasRepository.kt

...kotlin/de/justjanne/libquassel/persistence/AppDatabase.kt

...otlin/de/justjanne/libquassel/persistence/BufferEntity.kt

...n/de/justjanne/libquassel/persistence/BufferRepository.kt

.../de/justjanne/libquassel/persistence/MessageRepository.kt