Add support for multiple-template items

[gabipetrovay]

DMS items should support multiple templates.

Adjust the queries such that the _tp property is an array of ObjectIds.

[ottiker]

This was already possible due to the ability of MongoDB querying arrays values with the "equal" operator.

var document_in_db = {array: [1, 2, 3]};
var query = {array: 1}; // this returns 2