Bug 19982: Switch single-column templates to Bootstrap grid: Patrons

Bug 19982: Switch single-column templates to Bootstrap grid: Patrons

This patch updates two single-column patron module templates to use
the Bootstrap grid:

- discharges.tt - The list of pending discharges. One or more
  discharges must have been made via the OPAC. From the staff client
  home page, look for "Discharge requests pending."

- members-update.tt - The list of pending patron updates. One or more
  updates must have been submitted via the OPAC. From the staff client
  home page, look for "Patrons requesting modifications."

Each of these pages should look correct, with a single centered column
with wide margins on either side. At lower browser widths the margins
should disappear.

Signed-off-by: Claire Gravely <claire.gravely@bsz-bw.de>
Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Jonathan Druart <jonathan.druart@bugs.koha-community.org>