TRUNK-3197: An option is added for each sort Obs to be in asc or desc order

**Description:**
> TODO: add an option for each sort item to be asc/desc
> File: /openmrs/api/src/main/java/org/openmrs/api/db/hibernate/HibernateObsDAO.java
> Line: 213

**@dkayiwa Daniel Kayiwa's advice:**
> My advice is that when iterating over the sortList parameter, for each non empty sort, check if it has a sort order and use it. Else revert to the default as the existing code.
> To give an example of the contents of the sortList: "field1 asc", "field2", "field3 desc".
> From the above, you would sort field1 in ascending order, you would sort field2 using the existing default, and you would sort field3 in descending order, and more.

From these sources, I've implemented the advice, please review.