Pagestate features

[blakebyrnes]

This PR integrates PageStateGenerator with an ability to export and then import into the client.

It also adds "resources" to the generator.

When a page state is imported, it's sent in a single command to the backend as a "Tab.assert". Tab.assert then installs dom checks into each Frame as needed, and then can request them by id. This is to reduce the bandwidth of sending across client->core and also core->browser when we generate large sets of diffs.

Also in this PR:

• Refactored some network handling across puppet/core
• Broke up core/lib/SessionState into core/lib/Resources and Commands
• Capture browser "load time" of resources so we know when they overlap with dom changes
• WaitForElement returns the matching element, waitForLoad/Location internally return the navigation that satisifies the request (this is mostly for internally tracking for now)

Bugs fixed from Timetravel enhancements:

• Duplicated hero isolated worlds created in Timetravel (this was due to accessing contentWindow before a frame was ready). This entire strategy of seeing if content windows are ready is unnecessary when driving with devtools apis, so I turned it into a flaggable feature.
• Chromealive command timeline was misaligned with MirrorPage timeline