URL filter, Popup filter: auto-correct feature

[HashidaTKS]

          idea: If URL was pasted and registered it, it might be better to warn it or auto-correct it in the future.

Paste https://webct.riise.hiroshima-u.ac.jp/riise-files/popupcheck.html, then click register it,
webct.riise.hiroshima-u.ac.jp was actually registered. (it might improve user experience)

Originally posted by @kenhys in #302 (comment)