Bug 34201: Restore sorting indicator on ERM tables

Bug 34201: Restore sorting indicator on ERM tables

DataTable Vue component keep the 'sorting' class on the th which display
the grey up/down icon over the blue icon which indicate the current sort
column

Test plan:
Create several agreements, notice that the list view is having the
sorting indicators (blue arrows) in the top right of the first column.
Sort the columns: asc, desc, combined sort (shift+click) and confirm
that the indicators are correct

Signed-off-by: Sam Lau <samalau@gmail.com>
Signed-off-by: Pedro Amorim <pedro.amorim@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>