Improve tablature -- tie-follow and harmonics

Improve tablature -- tie-follow and harmonics

Create tab-tie-follow-engraver to display tab-note-heads
  as cautionary after ties and before slurs and glissandi

Make new tab-note-head callback that handles harmonic and
  cautionary display of tab-note-heads

Eliminate tab-harmonic-engraver and HarmonicParenthesesItem

Add 'harmonic-properties and 'cautionary-properties to
  TabNoteHead 'details

Add harmonic by fret and harmonic by ratio to tablatures

Center TabNoteHead columns, instead of left-justifying them.