Add support for multiple columns with sortDirection definition

[uap-universe]

Current Behavior

sortDirection can only be successfully specified for one column

Future Behavior

sortDirection can be specified for an arbitrary number of columns.
The order in which the sort options are applied, is from left to right.

Benefit

Sometimes you want to sort the table by default across two or more columns (e.g. last name, first name).
The only way this is possible now, is to wait for the table to load and call setSort() on the data source after initialization.
This is quite cumbersome. It's still necessary when you want to chose a different order in which the sorting is applied, but in most cases, people would want the table sorted the columns from left to right. The possibility to specify that via the settings removes the need for extra initialization code.