Clarify/correct "Leave Blank" button and "Allow Skipping" functionality

Currently, the following functions are true (or seem to be true) in a quiz:

1. If the "Allow skipping" function is enabled, a "Leave Blank" button is added to the bottom of each question
2. If the "Allow jumping" function is enabled, users can move to questions in any order using the navigation bar, or the answer sheet
3. "Allow jumping" cannot be enabled without "Allow Skipping"
4. Selecting the "Leave Blank" option on a question saves a "blank" answer on the question, so that it appears answered on the answer sheet
5. With the "Allow changing answers" function turned off, revisiting a question which was previously left blank does not allow you to change that "blank" answer. All other answer options are greyed out. Additionally, the "Next" option is not allowed, as it does not recognize "blank" as an allowable answer
6. In a quiz where answers cannot be changed, "Leave Blank" essentially becomes "Leave Blank Permanently (for this submission)"