Update Styling

The following estimation text is copied out of the High Level solution document:

20 hours of work for the UI styling (use 7.10 hippo theme, check the ~250 html files currently included in Essentials for necessary updates. Note: currently, we’re the only party contributing plugins to Essentials. When this changes, backwards-incompatible styling changes may break 3rd party plugins (they would break our plugins too, but we’re in a better position to anticipate). Hence, such changes should be made cautiously.