Viability: Start date of test

GG database schema has testedDate which represents the end date of the test, but does not have one for the start of test. By including started_date we can display the number of days the sample has been in the test, making it easier to follow the protocol.

Add to InventoryViabiltiy:

/**
 * The date when viability test was started and seeds sown.
 */
@Basic
@Column(name = "started_date", nullable = true)
private LocalDate startedDate;

/**
 * The duration of the test since its start (in days)
 */
@IgnoreField
@Formula("datediff( day, started_date, isnull( tested_date, CURRENT_TIMESTAMP) )")
private Integer durationInDays;

Note the use of LocalDate. I'd like to see if it also works with the SOAP protocol.