Moved some API classes into packages.

briar-tests/src/org/briarproject/TestMessage.java

...ts/src/org/briarproject/db/DatabaseComponentImplTest.java

briar-tests/src/org/briarproject/db/H2DatabaseTest.java

.../org/briarproject/plugins/ConnectionRegistryImplTest.java

...-tests/src/org/briarproject/plugins/DuplexClientTest.java

...-tests/src/org/briarproject/plugins/DuplexServerTest.java

briar-tests/src/org/briarproject/plugins/DuplexTest.java

...g/briarproject/plugins/bluetooth/BluetoothClientTest.java

...g/briarproject/plugins/file/RemovableDrivePluginTest.java

...s/src/org/briarproject/plugins/modem/ModemPluginTest.java

...ts/src/org/briarproject/plugins/tcp/LanTcpClientTest.java

...ts/src/org/briarproject/plugins/tcp/LanTcpPluginTest.java

briar-tests/src/org/briarproject/sync/ConstantsTest.java

...rg/briarproject/sync/SimplexMessagingIntegrationTest.java

...src/org/briarproject/sync/SimplexOutgoingSessionTest.java