Support configurable persistent parameters.

New advanced config option `advanced-persistent-params`. When set, URLs are modified to include the parameters.

This implementation differs from #134 by supporting loads and prefetches in addition to navigations. Also, instead of the config being of the form `?abc=def&foo=bar` it omits the leading `?` because it may be appended to a URL that already has params. The leading delimeter is determined at runtime based on the presence of params on the given URL.

Closes #134
You'll need to update the `handleClick_` functions as well to catch all sources of navigation.  And maybe add a comment to the `handleHistory_` function about _not_ adding the params there to prevent duplication?