Navigation fixes

This PR contains two fixes for back / forward navigation and one for history database cleanup (amended history changes to 'Add a unit test for clearing tabs and history'). 

1) Do not treat initial page load as navigation. Initial page load must only update the url for the active page.
2) Fix back / forward navigation loading after browser restart

I think that 1) has been there always. I'm not 100% though. Due to this there was an incorrect link data when a new tab was created.