[views] new cubicweb logo (closes #3803681) - add the new CubicWeb logo - use it as a css (background-image) - change the color of the header bar (gradient made with css)

from os.path import join
assert __file__.endswith(join('scripts', 'script2.py')), __file__
assert '__main__' == __name__, __name__
assert ['-v'] == __args__, __args__