pass the whole descriptor instead of filter name

Change-Id: I874e53a00d48ba84588126c1ecdb90c801a9b1d6
pass media descriptor to import functions

Change-Id: I0c3e9c7ba83ef886958789706929b2eede30c343
generalize ImportFilterBase a bit more

Currently there is a nearly exact copy of that class for every ODF
document type. That suggests that it might be a good idea to use a
template :-)

Change-Id: I2a24eb5bd63cc584569a948df63266c7eb703bd3
convert wpftcalc to use ImportFilter base class

Change-Id: I6692aee51753cddf57aaca1b7b7a94afafe60a9d
use MediaDescriptor to get input stream

Change-Id: Iecc7f373d0d352281b53324ef8824c5d7073fe8a