Change create order method to use a query to find actual products on shoppingList

It performs better, and also if we load all the products in the shopping
list in the create order method, we go beyond the 5 entity groups per
transaction limit of gae (it would load all the products and categories
associated to the shopping list items, that are each in its own root
entity group)
added objetify filter to web.xml
Modified helper scritps to run and debug app
Added Category to initialization servlets
Test super básico de front con angular