SVGHMI: add support for multiline widget declaration using svg:desc.
Declaration started in inkscape:label and interupted by a '\' can be continued in the description field.
After an empty line, the rest of the description field is left for description text.
[TOPOLOGY]
NetName=None
Nodes=0x01
Node64Present=0x01
Node64Name=micromod
Node64DCFName=PEAK MicroMod.eds
EDSBaseName=eds