Support multiple investigations / tabs

[nl5887]

No description provided.

[Thomas-Kuipers]

This is currently hard to do because we're using local storage for configuring the datatsources, fields, etc. Local storage is shared between tabs.

If we feel that having different config settings between tabs is important I think we should move away from putting this in local storage automatically, perhaps only when you click 'save', or maybe even stop using local storage at all. Instead of local storage we can rely on the config being in the URL and the export/import JSON. Not sure what to do here, we should discuss.