Fixes #6 generate nice URLs.

Avoid to escape most of the common characters used like []<>/+;...
Fix hide if successfully loaded initially.
Update image title.
Fix #9 work without JavaScript.
Refactor: Split controller and view.
Fix #8 do not auto-collapsed on home page.
Fix #10 add .png extension to image URL.
Fix #7 support sequence diagrams.

Old URL         New URL
/               /
/edit/*         /class/*
/image/*.png    /class/*.png
--              /sequence/*
--              /sequence/*.png
Fix #5 support SVG image export.

Also show the URL below the image on hover.
Reduce on image hover hit area.
Align input form on top for narrow long diagrams.
Make SVG export more discrete.

Instead of having two input fields for PNG and SVG,
simple have a link to the SVG image in small text.