Move the social media icons to plugin assets

[UTCGilligan]

Icon images should be moved to assets folder, vs. full paths from elsewhere. Campusweekly template has them done correctly for static paths; the other templates do not. Campusweekly also uses different icon styles than the other templates, which use either buttons or images, depending on style. Might need to change all of the templates to be more consistent with the new Campus Weekly responsive template.