Adds 'pod try' support to the search sheet

Adds a  "Try" button to the search sheet which executes "pod try" for the selected pod. A couple things to note:

1. 'pod try' isn't available before 0.29.0. The current implementation should show an error, but we could spend more time on that if that were a common case. It seems like most users would be on 0.29.0 though?
2. We should make sure that all the possible outputs of 'pod try' are covered. For example, a couple cases: the pod 'boxBlur' doesn't have a project, the pod 'LMAlertView' has multiple projects, the pod 'DTTableViewManager' crashes cocoapods (whoops!).
3. There is currently no way to cancel the pod try. It would be good to cancel it when the user closes the search sheet, but this seems like it would require some modifications to DSUnixTask?