Make article dashboard filters send correct search params

Category, author and published date filters on Article dashboard
were not correctly filtering.

Updates to send as part of search hash instead of GET query as
the latter was still showing "all" for each respective filter.

This now matches up with article state (published, draft, etc.)
and will restrict listings as expected.
Merge pull request #115 from randomecho/article-dashboard-filters

Make article dashboard filters send correct search params.