Bug 32087: Consistent classes for primary buttons: Course reserves

Bug 32087: Consistent classes for primary buttons: Course reserves

This patch makes changes the button markup in course reserves 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 course reserves pages to confirm
that everything looks correct. In most cases there are no visible
changes.

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