Templates: add a descriptive label for Org Name

We have found too many cases where users have been confused over what
should be entered into the Organisation Name field.

Users too often overlook 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.
Merge pull request #174 from University-of-Auckland/develop-explain-org-name

 Templates: add a descriptive label for Org Name