Use real DOM for testing (1 of 2).

New JS library `spf.testing.dom` appends elements to the document to be used in SPF tests.

Use this on response_test. Next and final part is to change resource_test.

Progress on #178
Support configurable persistent parameters.

New advanced config option `advanced-persistent-parameters`. When set, URLs are modified to include the parameters.

Parameters are appended prior to loads and prefetches in addition to navigations. The format of the config should be "abc=def&foo=bar" without a leading "?". The leading delimeter is determined at runtime based on the presence of params on the given URL.

Closes #134
Merge pull request #180 from rviscomi/persist-params

Support configurable persistent parameters.
Merge pull request #190 from rviscomi/dom-test

Use real DOM for testing (1 of 2).