Transmog appareance collection

Add in the wordpress administration panel of the user, next-to the Characters, a panel for "Transmog Collections".

It should show the collection items per account and, selecting a character and an item of the saved ones, the 3D character viewer with the related item selected.

Structure table for retrieving the item per account_id:
```
SQL
CREATE TABLE IF NOT EXISTS `custom_unlocked_appearances` (
`account_id` int(10) unsigned NOT NULL,
`item_template_id` mediumint(8) unsigned NOT NULL DEFAULT '0',
PRIMARY KEY (`account_id`, `item_template_id`)
) ENGINE = InnoDB DEFAULT CHARSET = utf8;
```

Mockup example:

I would like to replace the "ITEM" with some good item list in a OR better, something like the picture below.


related to https://github.com/azerothcore/mod-transmog/pull/72

Review the related mod-transmog pull request and the WordPress administration code that renders the Characters panel. Trace how account data and item records are currently retrieved before deciding where the Transmog Collections panel and 3D viewer should connect. Done means account-specific saved appearances can be browsed by character and item, with the selected item shown in the viewer.

Written by the indexing model from the issue text.