Change API for Note, Measure, and SheetMusic

Functions changed to inline if it was just 1 line of code.
Functions are const if they do not change member variables.

Changed removeLastNote in Measure and removeLastMeasure in SheetMusic to remove an element at a given index.
Parameters are now const pass by reference.
Removed the getAllNotes  vector in Measure andgetAllMeasures in  SheetMusic. Use the overloaded [] instead.
namespace std is no longer used.