Fix For Viewing Cached Jar Files In Jar Viewer

Previously if I double-clicked on a JAR file hosted in a remote repository in the Repositories view, nothing would happen.

Nothing would happen because it is not possible to create an IFile for a file outside the Eclipse workspace.

To fix I changed RepositoryBundleVersion to return a File if the IFile could not be created.

I then changed the Repositories view to support both IFile and File (File is converted to an IFileStore). Note that whilst it works I am not sure it is the right way to do this (e.g. getAdapter(IFile.class) apparently can also return a File?, rather than supporting Files and IFiles would it be better to just use Files?).