Typo fix

image_attributes.inx: mark more strings for translation; update POTFILES.in

Add extension to set attributes for bitmap images (bug #1357808) Inkscape >= 0.91 adds the attribute 'preserveAspectRatio' to imported bitmap images, and sets it to 'none' (to support non-uniform scaling). Unlike older versions it also respects the attribute for rendering. This change may break Inkscape documents with embedded or linked bitmap images which had been created with older versions of Inkscape (the images do not have the attribute set, and thus default to 'xMidYMid' with enforced uniform scaling). The extension allows to add the attribute to selected or all bitmap images in the current document (including bitmap images used as masks, which are stored in the <defs> section).