Added a call to setCodeInvalidated() to key setters on all core classes
(resposible to represent database objects) in order to keep the their
cache syncronized with the current configuration.
Created a new global (and environment) variable for samples directory.

Created two new sample models.

Sample models can be now loaded direclty from the central widget.

Source code dialog now optionally appends the SQL of permissions of the
current object.

Enhancement on the messages of model validation output.

Minor fix on object's schema files to correctly generate the appended/
Merge branch 'cached-code-improvements' into develop