µBlock logo refinement and browser icon organization

This includes a new, refined µBlock logo, rendered more coherently
and consistently for different sizes and display pixel densities.
The Safari build script has been modified to bundle appropriate
resolutions. The Firefox build script was slightly changed to
adhere to the naming convention. The Chrome manifest was
modified/ammended slightly to take advantage of new renderings.
README's beginning has been modified to be nicer and more
minimal.
Other than the logo's slightly refined look and having better
resolution on different browsers and setups, this should have
no effect on the user experience or further development.

tools/make-firefox.sh

@@ -16,7 +16,7 @@ cp -R src/js $DES/
 cp -R src/lib $DES/
 cp -R src/_locales $DES/
 cp src/*.html $DES/
-mv $DES/img/icon_128.png $DES/icon.png
+mv $DES/img/browsericons/icon128.png $DES/icon.png
 cp platform/firefox/vapi-*.js $DES/js/
 cp platform/firefox/bootstrap.js $DES/
 cp platform/firefox/frame*.js $DES/