a) fix vmldrawing.vml for xlsx export ( changed from frame to textbox, added
support for shadow element with attributes, shadow color, shadow obscured )
b) use proper fillcolor attribute
c) detect whether note/comment is shown on import
d) export state of note ( shown/hidden )

text position still not perfect, we still are missing some attributes to control
that.

Change-Id: I59b446175217479ce7960287aa540df8c6b2b1ea