Gapfill gapfeedback branch

Per gap feedback.

https://github.com/marcusgreen/moodle-qtype_gapfill/tree/gapfill_1.95_with_gap_settings

This branch allows a teacher to set up feedback for each gap based on if the response was correct or incorrect. The question editing form has a new Edit Settings button under the questiontext field. When this is clicked the background of the questiontext field turns dark and modification of the text is disabled. Clicking on text that is delimited to become a gap will pop up an editing form with fields for correct and incorrect response. There is an implied assumption that the text within the braces is unique. If two gaps have repeated text they will show the same feedback.

This feedback will be displayed inline with the text once the user has completed answering the question. It will display as expected on mobile devices and in the mobile app. A future release may add the ability to give feedback according to what answer the students have given. It is not designed to show images and the image button is disabled when editing the feedback. It will accept urls within the feedback.