Arrange of blocks in nested areas problems fix

The ccm_saveArrangement javascript function parses all the div.ccm-area and, for each one, retrieves its children div.ccm-block.
This is fine, except when there are nested areas: the same div.ccm-block can be a child of one area and a grandchild of another area (I've seen this problem with the area_splitter block).
This patch ensures that each block is passed just once to the ajax request (obviously associated to the nearest parent area).