Changed return type in model queries, added tests for model object

As we discuss with Tulio, he recommend to return an Array as result of the queries methods in the baseModel, since I think is better to return the PDOStatement I added methods to return the pdo statement and wrappers to return the Arrays.

An hydrate method was added to the BaseModel to override in the derivated objects the how the hirdation must be done. 

Pre and Post Hydrate hooks were added too.

Added test suite for models