feat: persistent search keyword in URI as permalink

[iori-yja]

This is intended to reflect search query in the URI so that people can exchange a link to the graph with highlighting some parts of it.

• On the invocation of "search" button, the query-string is changed by history.push() (pushState() in html5)
• With "clear" button, the query-string in the URI is cleared, as well as the result and input box.
• With a change of URI (such as navigation transition or direct typing), search result and input box respond to the new query.