Include query parameters in datagrid pagination links.
The datagrid pagination links had some implementation for preserving query

parameters, but it wasn't very complete. The review board code made sure that

the "user" and "group" parameters were part of it, but that lost all the other

things like sort order and show/hide closed.
I've removed the reviewboard implementation for "user" and "group" (in a

separate change) and instead generalized our existing `get_url_params_except()`

method (from `Column`). Because I hadn't realized that this method exists, I've

also included a refactor from my previous similar API change to use the new

generalized util method.
Other consumers of the datagrid who set extra_context['extra_query'] will be

unaffected by this change because it will overwrite the one that this adds.
Testing done:

Added a bunch of review requests, and checked that the pagination links

preserved "sort", "view", and other query parameters.
Fixes bug 1155.

Added a bunch of review requests, and checked that the pagination links

preserved "sort", "view", and other query parameters.