Update song_editor.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update piano_roll.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update AutomationEditor.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update song_editor.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update piano_roll.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update bb_editor.h

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update engine.cpp

A better way to update the play button icons, which requires less "if" checks and method calls in total.
Update bb_editor.cpp
Update AutomationEditor.h
Merge pull request #290 from M374LX/stable-0.4

Better way to update play button icons