add persistent query and paging

[crsct]

closes #45 by adding the base64 encoded query to the url

[lukasjelonek]

The current code requires only minor changes, but I think it does not implement a robust persistent navigation yet.

• It is possible to restore the search when reloading or coming from another page, but it is not possible to move back/forward on the history of the search page, e.g. the pagination information is part of the url, but going back to a previous page via the browser back button does not work.

• Classically search parameters are encoded in the query-part of an url. I propose to do this here as well, instead of having them as a part of the path. It might also be better to have the primitive types in plain text in the url, e.g. /search?offset=0&limit=20&query=<encoded query and ordering>, as this allows manual override for expert users.

[lukasjelonek]

I observed the following changes:

• The search is executed everytime, even on the first page load. Previously it was required that the user presses the search button
• Everytime the page is reloaded, two search requests are send to the server
• When the second page is opened and the page is reloaded, it loads the first page
• When the second page is opened and the back button is used, the second page is reloaded

The network traffic suggests that one of the two requests requests the current page and the other requests the expected page. Getting rid of the first one should eliminate most of the problems stated above.