Add support for negative lookups to constraints.

[Clorith]

Constraints are used to specifically state if am entry should be anonymized, but there are cases where the opposite scenario is needed, where an explicit declaration should not be anonymized.

This PR introduces the concept of negative constraints, specifically not like (or just not and similar shorthands), when a not rule is hit, it will not perform anonymization for the given value, this can be useful for example when needing to anonymize, but wanting to keep your username and password for your personal account.

Taking the example above, the following field rule would only replace the username and password for accounts that do not have the username marius:

{
  "tableName": ".*_users",
  "fields": [
	{
		"field": "user_login",
		"position": 2,
		"type": "username",
		"constraints": [
			{
				"field": "user_login",
				"position": 2,
				"value": "marius",
				"compare": "not like"
			}
		]
	},
	{
		"field": "user_pass",
		"position": 3,
		"type": "password",
		"constraints": [
			{
				"field": "user_login",
				"position": 2,
				"value": "marius",
				"compare": "not like"
			}
		]
	}
}

It is of course still possible to mix multiple constraints, but as soon as a rule that would prevent anonymization is found, it will short-circuit the remaining rules.

The example above is bad, because it looks for the user_login and needs it to not match a value, this could potentially suddenly trigger based on an anonymized value put in, and should instead be matched against a later column ( user_email in field 5 for example, but left it like this intentionally for emphasis).

In addition to the not like, two other entries are also found now: regex and regex not like. The explicit not like variant is because Go regex does not support negative lookahead or lookbehind, so it can not be used to do a negative lookup within a single rule type.

[PeterBooker]

LGTM! 👍