Revisit Router implementation

[kravets-levko]

Based on discussion here.

When implementing Router we assumed that page controller should be bound to URL path fragment and reloaded only when path changes. Watching for URL query parameters should be responsibility of each controller. That was a sort of optimization, but looks that it's not relevant since Router has a different behavior for history PUSH/REPLACE events.

The idea is to update Router and make it passing URL query parameters as props to controller. When parameters change (for the same URL path) current controller should be updated with new parameters.

Two places that need extra attention:

• ItemsList component (and all pages based on it): currently it does not watch URL changes by default, but it definitely should.
• Query Source page. There is a behavior that depends on optimization mentioned above: when saving new query, URL is updated but page controller should stay the same. Proposed Router behavior shouldn't affect this, but when implementing it we should keep this in mind.