Bug 32094: Consistent classes for primary buttons: Serials

Bug 32094: Consistent classes for primary buttons: Serials

This patch makes changes the button markup in serials templates so that
all submit buttons and any buttons that should should be styled as
primary buttons have the Bootstrap class "btn btn-primary."

To test, apply the patch and view serials pages to confirm that
everything looks correct. In most cases there are no visible
changes.

Signed-off-by: Katrin Fischer <katrin.fischer.83@web.de>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>