Notification for "Is Visa Required"

== Original Description ==
If the "Is Visa Required" field is checked and no record is entered, then it should a notification whenever the contact page has been visited. Need to add an Activity Notification to the Dashboard, and to periodically email a reminder.

== Updated Description ==

• Create activity types, "Visa Expiration"
• Implement a helper function, CRM_HRVisa_Activity::sync($contactID) to:

• Determine if "Is Visa Required" is true or false
• Find the latest visa
• Find/update or create an activity of type "Visa Expiration" (given the $contactID). There should be 0-1 records. If multiple exist, take the last (chronologically) and log an error.
• Set the activity_date_time to the expiration date of the latest visa
• Set status to "Cancelled" if an activity is found but not required
• Set status to "Scheduled" otherwise

• Add hook_civicrm_custom to call CRM_HRVisa_Activity::sync($contactID)
• During hook_install/enable/disable/uninstall, setup a weekly scheduled reminder for activities of type "Visa Expiration"
• Upgrade: Find all contacts who require visas and run CRM_HRVisa_Activity::sync($contactID)
• Add unit-test