oox: GrabBagStack: add method isStackEmpty

Change-Id: Iec563762e7be7fb6e2d5501fe5efeb88093793cb
oox: handle all w14 text effects at groupshape import

When dealing with groupshapes, the responsibility to process the
w14 text effects elements is in oox. This commit adds the code
to handle all elements and its children elements and attributes and
puts the values into a CharInteropGrabBag.

Change-Id: Iafb8759bd60e0ee831296dc2d9159f4311ad5403
editeng: Add CharInteropGrabBag to editeng.

Change-Id: I91c816499f463febc536d79e4a9fd9804f74df00
writerfilter: stylistic change to TextEffectsHandler

Change-Id: I5be926394dd97897dfb5ef3d4c03bb9ad9865a35