Improve Lessons Checklist Functionality

This ticket is for the following Checklist improvements:

• Ensure leading and trailing spaces are removed from Checklist Titles
• Ensure Checklist Title's are not all spaces
• Add the ability for Checklist Items to Link to Other Items
  • Only Link to items on current page
  • Only link to required items
  • Checklist Items, which are linked, are checked when the student visits the page & the requirements are met
  • An item may only be linked to once per checklist
• Improve checklist item parsing to use a JSON library
• Change Other Checklist sorting to be case insensitive
• Hide Checklist Group Header section if no groups

Screenshots (descriptions under the image):

The first item is unlinked and the second item is linked.

Clicking on the Link icon brings up a dialog which allows users to link items. The "Assignment" link icon was pressed showing the above dialog.

The above image shows having clicked on the "Unlinked" item's link. The dialog shows that the "First" assignment as all ready linked, and may not be linked to.

A tooltip is shown on hover which let's users know that an item is linked (this is the instructor view, the tool tip content is the same for instructors / students).

The tool tip shown (on hover) when a linked item has been completed.