1.4 tiny requests

[Rune Zedeler]

Now as 1.4 is on the way there are some small things it would be nice to change 
in the last minute:

- Instrument_name_engraver defaultly added to Staff, PianoStaff, etc. (Never 
really understood why it was turned off in the first place)
- Script.padding defaults to 0.3 - the maximum you get without destroying the 
staccato-dots. (Oh, fermatas look so crambled with zero padding)
- If it's not too hard: An official way of adding a metronome marking. (It is 
really hard to do in the hacky way if you have chord-names in top of your score)

-Rune