Changed 'output_material.py' to 'output.py'. FILESYSTEM.

This commit changes all output_material.py modules to just output.py.
Output modules are found in all material packages.

FILESYSTEM: you should change any output_material.py modules in your score
packages to output.py.

Here's some code to effect the renames:

    for directory_path, subdirectory_names, file_names in os.walk('.'):
        for file_name in file_names:
            if file_name == 'output_material.py':
                file_path = os.path.join(directory_path, file_name)
                new_file_path = os.path.join(directory_path, 'output.py')
                command = 'git mv {} {}'
                command = command.format(file_path, new_file_path)
                os.system(command)

IMPORTS: you should also change import statements from ...

    from output_material import tempo_inventory

... to ...

    from output import tempo_inventory

... instead.

You can use ...

    ajv replace 'output_material import' 'output import'

... to do this.