Support Portal state via url params

This is an updated to an earlier version on supporting query history.

This feature is intended to be similar to Neuroglancer's ability to recreate its complete state from url parameters.

For the Portal, using a url w/state embedded should

- Repopulate the query
- Execute the query
- Maintain neuron selection in the viewer for any neurons that were selected with the caveat that executing the search at a later time may result in neurons that were not present before or neurons that have been removed