Bug 27876: added sr-only to caption of table in Charges page

Bug 27876: added sr-only to caption of table in Charges page

Made the "Your charges" caption of the table in the Charges page of the
OPAC hidden and for screen-readers only so that it takes out redundancy.

To test:
1) Apply patch
2) Go to OPAC
3) Go to Charges page
4) Ensure that there is no visible caption above the table that says
"Your charges"
5) Check that the code has the caption still with sr-only class

Sponsored-by: Catalyst IT
Signed-off-by: Henry Bolshaw <bolshawh@parliament.uk>
Signed-off-by: Nick Clemens <nick@bywatersolutions.com>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>