fix bug 834296, 834297: Alternate Bleach whitelist switch

* New Constance settings to allow runtime changes to alternate Bleach
  whitelists

* ?bleach_new query parameter for authenticated users that switches
  document view over to the Constance-defined Bleach whitelists

* Flag in DocumentManager.clean_content() to use Bleach whitelists
  defined in Constance settings

* Tweaks to kumascript.post() processing chain to use the
  alternate whitelist flag

* Tests
Hide empty fields in comparison
Merge pull request #838 from darkwing/compare-fields

Hide empty fields in comparison
Merge pull request #837 from lmorchard/834296-waffled-bleach-whitelist

fix bug 834296, 834297: Alternate Bleach whitelist switch
fix bug 805058 - Add navigation to add, list docs
Add February and April 2013 Derby copy.
Merge pull request #840 from openjck/derby-copy-2013-02

Add February and April 2013 Derby copy.
Adding another flag to the docs
Merge pull request #841 from darkwing/instruction-updates

Adding another flag to the docs
Merge pull request #839 from darkwing/nav-805058

fix bug 805058 - Add navigation to add, list docs