Fixes for MIDI import. Instruments with the same channel

Fixes for this issue: http://musescore.org/en/node/41011
Now it looks like http://wstaw.org/m/2014/12/08/plasma-desktopYs1927.png
and http://wstaw.org/m/2014/12/08/plasma-desktopFX1927.png

Also some tests for Grand staff instruments detection were added 
to do not break existing functionality if it is correct.

The list of organ 3 staff MIDI instruments I've taken from here: http://musescore.org/node/22548