Enable Alert infrastructure

We'd like to enable the Alert infrasruction for OpenMRS 2.0.

Ideally these alerts will show in the header and could optionally contain a hyperlink directed to a certain page relevant to the alert. E.g. When a radiology study is ready for one of the provider's patients, the provider will see the alert in the header and can click on the link in the alert, which would bring them to the patient's page.