InstrumentView: include QIcon header file

Otherwise implicit conversion fails when calling setWindowIcon().
InstrumentTrackView: manage general settings widget using layouts
InstrumentTrack: added pitch range spinbox
Revert "Extensions for peak controller. Fulfills request 144."

The change breaks existing projects that use PeakController (i.e. they
sound completely different which is not acceptable) as there's no sane
default value for the new amount multiply model (why do we need it at all
BTW instead of just advancing the range of the existing amount model?) and
the changed math results in calculation of completely different RMS values.

This reverts commit 5e8dbb615728b89775a2ca6252f83623d4251e86.
save solo states for tracks
Merge pull request #58 from bhattigurjot/stable-0.4

[Patch] Save solo states for tracks