fix: explicitly set favicon in all HTML pages [#1105]

In pages such as the update page, the ABP favicon is not displaying in Firefox. This is because we are not setting any favicon on any HTML page, save for the options page parent frame.

It works in Chrome because it pulls a default favicon from the manifest.json file, but this behavior is not documented.

Since we don't use any templating language for our HTML page, the easy solution is to explicitly set the favicon in every single page.

Before:

After:

Related to #1105 (closed) - more info about debugging the problem in this issue comment