Allow changing browser hash from python side.

[mturoci]

via @maxjeblick

Needs discussion: It might be worth to allow controlling browser hash from python SDK. E.g.:

q.args['#'] = 'new-hash'

cc @geomodular @lo5

[mtanco]

this would be nice for things like tour where the hash nav gets "off" if you use the prev, next buttons

[lo5]

You can use the meta card's redirect for this.
https://h2oai.github.io/wave/docs/examples/meta-redirect

page['meta'] = ui.meta_card(box='')

# Redirect to a hash.
page['meta'].redirect = '#widgets'
page.save()

We need a simpler wrapper API for this, though.