Refactoring: shorter class names.

api/net/sf/briar/api/plugins/BatchPlugin.java

api/net/sf/briar/api/plugins/BatchPluginCallback.java

api/net/sf/briar/api/plugins/Plugin.java

api/net/sf/briar/api/plugins/PluginCallback.java

api/net/sf/briar/api/plugins/StreamPlugin.java

api/net/sf/briar/api/plugins/StreamPluginCallback.java

components/net/sf/briar/plugins/AbstractPlugin.java

...nents/net/sf/briar/plugins/bluetooth/BluetoothPlugin.java

components/net/sf/briar/plugins/file/FilePlugin.java

...nents/net/sf/briar/plugins/file/RemovableDrivePlugin.java

...nents/net/sf/briar/plugins/socket/SimpleSocketPlugin.java

components/net/sf/briar/plugins/socket/SocketPlugin.java

test/net/sf/briar/plugins/bluetooth/BluetoothClientTest.java

test/net/sf/briar/plugins/bluetooth/BluetoothServerTest.java

test/net/sf/briar/plugins/file/RemovableDrivePluginTest.java

test/net/sf/briar/plugins/socket/SimpleSocketPluginTest.java