MIDI import of drums: clean up rests and ties

The goal of the new option is to minimize number of rests and ties on drum staves for cleaner notation. 
We talked about it on IRC earlier (September 28).
Also Sibelius has this feature. 
The rests/ties deletion is turned on by default.

Current name of the option is "Remove rests and ties between notes".

Before - drum sets with rests and ties:

https://docs.google.com/file/d/0B5alKuFoSol2Z3pCcWtmWVJ4UHM/edit?usp=sharing
https://docs.google.com/file/d/0B5alKuFoSol2cUkwN3p5VzVYdkk/edit?usp=sharing
https://docs.google.com/file/d/0B5alKuFoSol2TXludE5CRWpidG8/edit?usp=sharing

After - very few rests and ties remaining:

https://docs.google.com/file/d/0B5alKuFoSol2clNrakI4T0ppOWs/edit?usp=sharing
https://docs.google.com/file/d/0B5alKuFoSol2dFRmLWYxMHJBb3M/edit?usp=sharing
https://docs.google.com/file/d/0B5alKuFoSol2NkZfaUxxdExFelU/edit?usp=sharing