Modified SetupFixture to save SQL dumps of fixtures when needed, make sure OmniFixture can be used w/ SetupFixture, and use SQL dump of OmniFixture in UI tests instead of running OmniFixture every time (so changes in fixtures do not result in changes to screenshots).
Merge pull request #349 from piwik/uitests_fixture_decouple

Decouple UI tests from fixtures by using SQL dump of OmniFixture.

Notes:

  - Add sqldump parameter to SetupFixture command that saves SQL dump of database.
  - Added SQL dump of OmniFixture (gzipped) and used by UITestFixture.