SOGo uses the name of calendar categories verbatim to construct a CSS
selector without escaping characters such as "/". This patch ensures
those selector names are properly escaped so calendar categories
applied to a calendar event match the according selector and appear
in the correct color.
This patch makes use of the CSS escape API which is supported by all
major browsers. See https://caniuse.com/mdn-api_css_escape.
Also see https://mathiasbynens.be/notes/css-escapes.
Leon Klingele
Francis Lachapelle