`Programming and Text Exercise`: Context menu issues

[terlan98]

• The context menu interferes with the highlights when the user keeps the finger on the submission content for too long before dragging. We should either solve this or disable it.

  highlight.context.menu.mov

• Also for programming exercises, we should remove the 'Feedback' option from the context menu. It's not available for other exercise types and can cause invalid selections and confusion.

This issue was found during the user study.