Refactor manager and tasks to remove reliance on files.

...roject/bramble/api/plugin/file/RemovableDriveManager.java

...arproject/bramble/api/plugin/file/RemovableDriveTask.java

...roject/bramble/plugin/file/RemovableDriveManagerImpl.java

...project/bramble/plugin/file/RemovableDriveReaderTask.java

...roject/bramble/plugin/file/RemovableDriveTaskFactory.java

...ct/bramble/plugin/file/RemovableDriveTaskFactoryImpl.java

...arproject/bramble/plugin/file/RemovableDriveTaskImpl.java

...project/bramble/plugin/file/RemovableDriveWriterTask.java

...ct/bramble/plugin/file/RemovableDriveIntegrationTest.java