ESSENTIALS-525: Restore folder picker tree functionality by using older version of angular-ui-tree.js.

ESSENTIALS-525: Replace the jQuery-based Library Screenshot carousel with an angular-bootstrap based one.

ESSENTIALS-524: Fixed licensing of skeleton package, and fixed paths of 3rd party artifacts in dashboard module.

    * modified all select boxes to use hippo.theme select (gallery, document wizard, selection plugin)
    * changed styling of above selects
    * removed licence notices (chosen)
- remove all less files and unused css files
- remove unused test-skeleton folder