TBA: Implement about:tor

Design: https://trac.torproject.org/projects/tor/attachment/ticket/25696/24309%20-%20TBA%20-%20Welcome%20Page.png

Onion circles implemeted in html + css:

https://trac.torproject.org/projects/tor/attachment/ticket/25696/onion_circles_pattern.html

Onion circles implemented in svg:

https://trac.torproject.org/projects/tor/attachment/ticket/25696/onion_circles_pattern.py

.png and .svg version were ready to be exported at ​​https://marvelapp.com/5981a4b/screen/44384308/handoff

more info: https://trac.torproject.org/projects/tor/ticket/25696#comment:15