UC14 [S2]: Detect Flu Epidemic

This PR implements the second sub-flow of UC14. This allows a healthcare provider to log in and see if an influenza epidemic is/was occurring in a given zip code at a given time. To do this, the influenza detection algorithm from the requirements was implemented.

In order to run the tests, enter the following commands:

1. mvn install -DskipTests
2. mvn test -Dtest=ViewDiagnosisStatisticsActionTest
3. mvn test -Dtest=ViewDiagnosisStatisticsTest
4. mvn test -Dtest=OVDiagnosesTest