REPORT-415 Add preview button to composition cohort query

The Preview button is in place and working - takes you to a preview page just like the editCohortDefinition preview page.But when you enter parameters and click the Run button from the Preview page it crashes with a null pointer exception.
However, the same thing happens to me when I click on the Run button in the editCohortDefinition preview page and the sqlCohortDefinition preview page. Also it happens to me when I click the Save as New button. So, maybe I'm entering the parameters 
incorrectly or something. Issuing pull request so you can take a look at it.