Add "Musical Score" to the available list of resource types

[mark-dce]

STORY
As a repository administrator, I would like to add Musical Scores to my list of valid resource types, so that composition majors can deposit their final projects.

ACCEPTANCE

• The list of resource types available under Additional Fields includes "Musical Score"

[bhavanaananda]

Solution: https://github.com/RepoCamp/backbus/tree/add_musical_score_to_avail_list