Added "wait" field in new task and edit task pages

Added UI control to set `wait` option in pa11y script. Updated test
cases.

[pa11y-dashboard issue
#127](https://github.com/springernature/pa11y-dashboard/issues/127)

route/task/edit.js

@@ -60,6 +60,7 @@ function route(app) {
 					task.name = req.body.name;
 					task.ignore = req.body.ignore;
 					task.timeout = req.body.timeout;
+					task.wait = req.body.wait;
 					task.username = req.body.username;
 					task.password = req.body.password;
 					var standards = getStandards().map(function(standard) {