This is a fix for #1280. Added lock around the access to the sound effect management lists. Also changed the use of HashSet in lieu of List.
Merge pull request #1282 from totallyeviljake/ISSUE_1280_R1

This is a fix for #1280. Added lock around access to management lists.
Merge branch 'develop3d' of https://github.com/mono/MonoGame into develop3d