Allow excluding directories from the model search with sensible defaults

In L5 (this is also backwards compatible/non-breaking with L4) your models now live in the base app directory - 
You also have a bunch of other directories at the same level that do not contain models Console, Exception, Http etc - 

These generate a lot of "xxx is not a model" message, this requests allows you to set paths relative to the base url (the same as model_locations) that classes found will not be added to the models array.

This is recursive so excluding app/Console will exclude app/Console/Commands etc.