improve styles after implementing new button icons
improve look and usablility

• make tag panel higher, more precise
• fix various details for input and button
• make tag_panel look cooler without border
• add setting is_open for highlighting open-tag-panel button depending on visibility
remove deprecated add_tag_panel

• this will not be used anymore because the tag panel has to be accessible in both admin and preview
add tag area to page detail

• analog to the tag_areas in the other detail widgets