Add Property Writeable to Image.File
Add Property Writeable to Image.File

Since we start supporting some file formats just for reading
(at least for now) the property Writeable is added to Image.File
to indicate if a file can be written back or not.

https://bugzilla.gnome.org/show_bug.cgi?id=621508

punker76/taglib-sharp,Clancey/taglib-sharp,hwahrmann/taglib-sharp,CamargoR/taglib-sharp,archrival/taglib-sharp,Clancey/taglib-sharp,hwahrmann/taglib-sharp,archrival/taglib-sharp,punker76/taglib-sharp,mono/taglib-sharp,Clancey/taglib-sharp,CamargoR/taglib-sharp