Modified dark theme

[mihak]

I changed the css of Vicuna dark theme a bit to make it a bit more consistent with my other dark-themed apps.
I don't know if this is of broader interest of community to potentially package it into a new theme, so here is a dirty preview hack how to install and comment.

1. install and select Vicuna theme - (or possibly any other non-default theme)
2. go to /usr/local/opnsense/www/themes/vicuna/build/css
3. replace main.css and tokenize2.css with the attached .css files
      (do a backup of originals, ok?  )
4. replace the default-logo.png in /usr/local/opnsense/www/themes/vicuna/build/images with attached .png
      (I didn't do anything dramatic to OPNsense image - made it less colorful and shrunk it to the size it should be at)

If you open the main.css, you will see how I am simplifying your own modifications; css variables to the rescue!

Let me know if I didn't re-color anything significant - there are still tons of hard-coded color tags in both .css files and I am cleaning them as I go...

Ah, here is also a screenshot of the theme among attachments below...

[mihak]

Whoops, this time with correct attachments!