Defer assigning plugin events

Overview

Allow time to pass before assigning events so that we can be more confident that the plugin UI has been added to the DOM.

Connects #1173

feb-08-2019 15-26-58

Run ./scripts/server, visit the site, and verify the existing plugins load correctly and that their UI buttons correctly trigger events.
Build the hawaii region on this branch: python build.py hawaii-region --framework-branch cpc/fix-plugin-event-assignment-2
Extract the resulting zip.
Comment out lines 177-178 in /geosite-framework-build/output/hawaii/plugins/ecological-effects-slc/main.js. This was a temporary fix to this issue.
Run a static server in the region directory.
Visit the site, close the help screen, make a selection in the plugin menu, then click the "Print" button.
Verify the print dialog appears on the first click.