convert button+JS to anchor in social network links

fix issue #9
remove .sitelink background image

.sitelink contains an image element that outputs the moodlelogo, adding it as a background attribute duplicates the output.
Merge pull request #25 from thedannywahl/issue9_social_network_links

convert button+JS to anchor in social network links
Merge pull request #26 from thedannywahl/duplicate_image_output

remove .sitelink background image