ECMS-5410 Drag&Drop UI looks not beautiful

Problem analysis:
  In Content Explorer, while user drags and drops nodes, there are some bugs:
   1. In Webview and Iconview, target node is not highlighted
   2. In container of moved node, all icons are in vertical line
   3. The container of moved node is too big.
Solution:
   1 ->  Highlight the target node
   2 ->  Icons should be in horizontal line
   3 ->  Reduce the size of this container