Consolidate dictionary generation code in one place for KeyChain access

[insha]

Something along the lines:

static NSMutableDictionary* NSMutableDictionary createQuery(id class, id service, id account) {
    ...
}

Providing we cover all the parameters for all the methods, such as kSecReturnData, kSecReturnAttributes, kSecMatchLimit, kSecAttrAccessGroup and not constrain the query.

[ghost]

I'm concerned that setting nil as a query parameter via a class method to create the query, may actually constrain the query, which is what I'm trying to avoid. Will need testing or advice - @YuanZhu-apple ?