Added support for serializing/deserializing query to/from URL query string

Now the filter state is instantly update to the query string as a query is being built. The query string format is based on the API 'shortcut' syntax (e.g. n_elements:gte=2).

The exclusive/inclusive element queries are a bit tricky to handle ATM, since they use entirely different fields. Would be great if the API could support an ':only'-prefix for elements. This would make it easy to switch between inclusive/exclusive mode (elements:only=Na vs. elements:all=Na).