Templates: add a descriptive label for Org Name 

We have found too many cases where users registering new organizations into FR got confused over what should be entered into the Organization Name field.

Users too often overlooked the example indicating it should be the DNS name (and did not read the tooltip) and entered a human-readable organization name instead of a machine readable one.

This patch hopefully fixes this source of confusion by adding a very explicit label - changing the ambiguous "Name" to "DNS Domain Name".

For this, we introduce a new label in messages.properties (```templates.fr.organization.label.name```), replacing the default ```label.name``` on pages specific to organizations: the _create, _edit and
_overview_editable organization templates.

All tests passed.