Experimental Header Navigation

[G-Ambatte]

This PR adds a button to the BrewRenderer. When clicked, this exposes the header navigation window, which lists all of the elements with IDs in the document. It generates this information by calling querySelectorAll('[id]') to acquire a list of all elements that have an id attribute, then parsing these for the following conditions:

• has the class page - depth: 0; text: 'Page' + page number
• is h1 through h6 - depth: heading value, i.e. h1 => 1, h6 => 6; text: innerText value
• all other elements - depth: 7; text: innerText value

From one of the documents in my local install DB:

CLOSED:

OPEN:

HOVERING OVER "PAGE 2: