Add ability to set foreignkey value without using setRelated

Since foreignkey is a single value, it should not need to be set 
using the setRelated function of the model and can be set like 
other fields. __set now calls setRelated if the field is in the relatives 
array.
move page app to builtins folder
move engine error handling to dedicated class
change management of urls with apps
update builtins for dealing with new app handling
updates to handling urls, fix tests
add single variable find and retrieve to request
remove unused methods from urlHandler
update tests for changed methods