Easy-digital-downloads: Customers/Customer meta table improvements

[JJJ]

(See #2256 for the original issue & discussion when this table was introduced.)

Currently:

id bigint(20) NOT NULL AUTO_INCREMENT,
user_id bigint(20) NOT NULL,
email varchar(50) NOT NULL,
name mediumtext NOT NULL,
purchase_value mediumtext NOT NULL,
purchase_count bigint(20) NOT NULL,
payment_ids longtext NOT NULL,
notes longtext NOT NULL,
date_created datetime NOT NULL,
PRIMARY KEY  (id),
UNIQUE KEY email (email),
KEY user (user_id)

Recommended:

id bigint(20) unsigned NOT NULL AUTO_INCREMENT,
user_id bigint(20) unsigned NOT NULL default '0',
email varchar(100) NOT NULL default '',
name mediumtext NOT NULL default '',
purchase_value mediumtext NOT NULL,
purchase_count bigint(20) unsigned NOT NULL default '0',
payment_ids longtext NOT NULL default '',
date_created datetime NOT NULL default '0000-00-00 00:00:00',
PRIMARY KEY (id),
UNIQUE KEY email (email),
KEY user (user_id)

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In English:

• Make bigint's unsigned because negative numbers should not be allowed in them
• Enlarge email from 50 to 100 to match what's now in wp_edd_orders
• Add default values everywhere, because they are NOT NULL
• Default value for date_created that is a properly formatted empty date string
• Remove the notes column, which we can move to wp_edd_notes with a customer note type and ID

Tangent

I noticed that wp_edd_customermeta has an un'prefixed customer_id column. This should now be edd_customer_id to avoid collisions and bugs with _get_meta_table() and to be brought up to speed with other work going into EDD3.

[pippinsplugins]

Remove the notes column, which we can move to wp_edd_notes with a customer note type and ID

This will require an upgrade routine to migrate existing notes over.

[sunnyratilal]

We should also remove the payment_ids column because the new edd_orders table will store a customer_id linking the two together nicely.

The current method also isn't best when deleting payments - we need to search the array to remove the payment ID (not very efficient if a customer has, say 1,000 orders) and then update the DB.

[sunnyratilal]

We'll need an upgrade routine that alters the name of the meta column from customer_id to edd_customer_id.

[cklosowski]

we'll also need an upgrade routine to handle the customer record re-creation for purcahses that had an email address over 50 characters, as the payment would have been successful, but the customer would not have been created.

[sunnyratilal]

Merged.