Setup icons style to fill using currentcolor

[ibirisol]

This change in the icons to support CSS properties in SVG was made by using the commands below (closes #229):

sed -i 's/style="fill:#000000;/style="fill:currentColor;/g' svg/isni.svg 
sed -i 's/style="color:#000000;/style="fill:currentColor;/g' svg/open-access.svg svg/pubpeer.svg
for svg in $(grep -L 'style=' svg/*); do echo $svg; sed -i 's/<path/<path\n       style=""/g' $svg;done
for svg in $(grep -l 'style=' svg/* | grep -v 'open-access.svg\|pubpeer.svg\|isni.svg'); do echo $svg; sed -i 's/style="/style="fill:currentColor;/g' $svg;done