Research into a @lit-labs/router replacement

[djarekg]

@lit-labs/router currently has very basic features and needs to be replaced with a more mature router with at least the following features:

• Guards
• Child routes
• Routing (Navigation) events - i.e. navigation start, navigation end, etc.
• Navigation transition APIs would be nice

Currently known routers to investigate:

• @lit-labs/router Fork and add required features
• vaadin-router
• lit-redux-router
• lit-element-router
• List of routers