Add Admin UI to delete existing H5P libraries

Setup Login as admin. Create a course with a forum. Enrol a teacher (t1) in the course. Add a new topic to the forum ("Admin's H5P content"). In the message, use the H5P button in the Atto editor to add the  arithmetic-quiz.h5p  content.  Save and check the H5P content is displayed as expected. Logout. Login as teacher t1. Add a new topic to the forum ("Teacher's H5P content"). In the message, use the H5P button in the Atto editor to add the  arithmetic-quiz.h5p  content.  Save and check the H5P content is displayed as expected. Logout. Testing scenario: Delete a library. Login as admin. Go to "Site administration / H5P / Manage H5P content types". Delete library "Transition". Access to the forum discussion "Teacher's H5P content". Check  the H5P content is not displayed. Several messages are displayed, one of them is similar to " missing-required-library : Missing required library H5P.ArithmeticQuiz 1.1 ". Access to the forum discussion "Admin's H5P content". Check  the H5P content is displayed as expected ("Solve these multiplication quizzes as fast as you can!"). Access again to the forum discussion "Teacher's H5P content". Check  now the H5P content is displayed as expected ("Solve these multiplication quizzes as fast as you can!").