Fix double output of mimesearch-summary

The execute method was calling a outputHeader(), and then calling
it's parent implementation which was also calling outputHeader()
causing double output.

Refactor class to use $this->getPageHeader() to output menus
before result list, as that appears to be what that method is
for.

Change-Id: Ic0a79cb73136e636f96e33859dadb384eca38255
Merge "Fix double output of mimesearch-summary"