UI improvements

[thoroc]

This is great, but there is 2 improvements I could see made to the UI when dealing with long documents:

1. the container where the 'add comment globally' is located should be sticky so scrolling down the page doesn't forces you to scroll all the way to the top to click on it
2. a sticky table of content should be on the left hand side of the page to allow easier navigation to the different sections.