fix a problem with themes containing secured first level layer groups wh...

...en using an url generated from permalink: using the theme passed in the url we retrive all the theme layersgroups and merge them with the permalink layergroups. to accomplish this, it was also needed to separate the defaultThemes from the themes automatically set in the url by the history.replaceState from loadTheme

fix https://github.com/camptocamp/cgxp/issues/549