Added a "Select and Close" button that can optionally be displayed only if a valid snippet is provided. Clicking the button causes an XRef search to be returned that selects the snippets on the currently selected tab.
Fixes feature request #77 "Allow snippets listed in dependencies dialogue box to be selected" (https://sourceforge.net/p/codesnip/feature-requests/77/)
