CMS-766 Content Types - Set specific icons for all "built-in" types

- added icomoon icons and css file
- updated TreeGridPanel and DetailPanel icon resolving methods
- removed contentstudio-preview-panel.css and used admin-preview-panel.css instead
- unified css and html temlates for grid and tree cells
- moved detailPanelInfo.html template from contenttype to contentStudio (as we don't have contenttype now)