Annotations Tools: Sharing Plugin Fixed with Proper URI

**Priority is HIGH for this PR since the course is currently live and the share functionality is not working properly.**

**Background:** This is a bug fix for ChinaX course (currently happening!!). There was a bug originally with how the URI was formed for the sharing mechanism when you had multiple annotation tools in a single subsection under different Units. 

**CMS Updates:** None.

**LMS Updates:** Minimal, the way the URL was created to bring you back to the correct annotation was fixed, also Daniel did not implement the one for images, but I used the fix from catch.js to fix it.

**Testing: ** Create an annotation (text, image, and/or video) and hover over it. A hover pop-up should display the annotation text along with a Sharing button. When that button is clicked the lightbox appears with links to facebook, twitter, etc. The only thing that has changed is that the url below should now contain an extra URL parameter to designate the Unit where the Tool is present. Activating that link in a new window should have one of the following results:
1. Text highlight will turn green and the page will scroll down to that line.
2. Image should zoom/pan to display the annotation
3. Video should start playing based on where the annotation's start and end times are. 
Comment? What does it mean if the length of this element is 0?