SMWQueryPage::getSearchForm() add search form

* Add search form similar to that found in Special:Categories used in [1]
* Add QueryPageTest

[1] https://gerrit.wikimedia.org/r/#/c/70041/

Change-Id: Ic008776070bae9e4d2c16223545ae4256546308f
Merge "SMWQueryPage::getSearchForm() add search form"