updated ui

vipra-ui/app/html/about.html

vipra-ui/app/html/articles/index.html

vipra-ui/app/html/articles/show.html

vipra-ui/app/html/articles/similar.html

vipra-ui/app/html/explorer.html

vipra-ui/app/html/index.html

vipra-ui/app/html/topics/index.html

vipra-ui/app/html/topics/show.html

vipra-ui/app/js/app.js

vipra-ui/app/js/controllers.js

vipra-ui/app/js/filters.js

vipra-ui/app/js/helpers.js

vipra-ui/app/less/app.less

vipra-ui/bower.json

vipra-ui/gulpfile.js

vipra-util/src/main/java/de/vipra/util/Constants.java