Bug 31888: Define save button as primary in Elasticsearch mappings page

Bug 31888: Define save button as primary in Elasticsearch mappings page

Like Bug 31810, save button in Elasticsearch mappings page is the most important action on this form, it should be yellow.

Test plan :
Go to Administration > Search engine configuration (Elasticsearch)
=> Check save button has class btn-primary and is yellow

Signed-off-by: David Nind <david@davidnind.com>
Signed-off-by: Martin Renvoize <martin.renvoize@ptfs-europe.com>
Signed-off-by: Tomas Cohen Arazi <tomascohen@theke.io>