Adjust to Dynamic DOMA

[ChrisERo]

Right now, extension works by waiting for some time (e.g. 800 milliseconds) and the highlighting text in website. This works well for static websites whose content is finalized by that time, but not so well for dynamic pages (those whose DOM may change over time, or at least after the expected length). This would result in a lot of text getting placed in missing section unnecessarily.

To resolve this issue. I propose adding some listener to see if the DOM changes (for reasons other than highlighting) and if so, perform a search (at least on the changed DOM nodes) for text in missing and highlight if found.

Not sure if this is a real problem the at needs fixing.

[ChrisERo]

Possible solution described here: https://stackoverflow.com/questions/3219758/detect-changes-in-the-dom
Here is the API that is employed: https://developer.mozilla.org/en-US/docs/Web/API/MutationObserver/observe
https://developer.mozilla.org/en-US/docs/Web/API/MutationRecord

[ChrisERo]

Possible idea:

1. Set up a permanent MutationObserver and observe body node (Element)
2. If no missing words, just return
3. For every update, look though list of added nodes for missingWords, highlighting when found
4. May need to filter based on modification type and avoid new nodes that are highlight nodes :)