extend load features/annotation menu option and drag'n'drop handler to recognise and load T-Coffee files

T-Coffee annotation should be imported using the 'load features/annotation' method rather than having a dedicated button on the file menu. Need to extend jalview.io.IdentifyFile method and various annotation loading routines should be extended to recognise and call the TCoffee annotation parser in the same way that jalview supports loading of a jnet concise file onto the alignment as annotation.