Rename classes and source files to have the GO prefix

[oleg68]

Aggording to #793 it has decided, that all GrandOrgue classes should have the single GO prefix.

1. All classes and files started with GOrgue should be renamed to start with GO (remove rgue).

2. All classes and files started with GrandOrgue should be renamed to start with GO.

3. The files should be renamed to correspond to the class names

4. The names of header files with these prefixes not containing any classes should be converted to lowercase with the prefix go_

5. Not to forget to rename include protection variables:

   #ifndef GORGUESTOP_H
   #define GORGUESTOP_H
   

   to

   #ifndef GOSTOP_H
   #define GOSTOP_H