MailingEventQueue - Use consistent short/camel-name.

MailingEventQueue - Use consistent short/camel-name.

Unchanged
---------

* XML: `xml/schema/Mailing/Event/Queue.xml`
* DAO: `CRM/Mailing/Event/DAO/Queue.php`
* BAO: `CRM/Mailing/Event/BAO/Queue.php`
* APIv3: `api/v3/MailingEventQueue.php`

Changes: Before
---------------

* TLDR: Inconsistent mix of `MailingEventQueue` and `Queue`
* `AllCoreTables` lists the short/CamelCaseName as `Queue`, which
  does not match the APIv3 name (`api/v3/MailingEventQueue.php`).
* When formatting results for `MailingEventQueue.create`, it
  uses `_civicrm_api3_basic_create(...'Queue')`. Again, that
  name does not match `api/v3/MailingEventQueue.php`.
  (Substantively, this means that it may call `Queue.getfields`
  to read extra metadata. But this returns an empty list...)

Changes: After
---------------

* TLDR: Consistent use of `MailingEventQueue`
* `AllCoreTables` lists the short/CamleCaseName as `MailingEventQueue`
  which does match the `api/v3/MailingEventQueue.php`
* When formatting results for `MailingEventQueue.create`, it
  uses `_civicrm_api3_basic_create(...'MailingEventQueue')`.
  This matches. (Substantively, this means that it may call `MailingEventQueue.getfields`
  to read extra metadata. As before, this returns an empty list...)

Comments
--------

In reconciling the conflicted names, I looked at both APIv3 and APIv4.
APIv4 does not expose an entity for this; so the Before+After ocuses on APIv3.