Framework core improvements

- xImageUpload crop mode fixed
- all the form validation methods were taken out of XyneoModel and were
added to a a validator class called XyneoValidate. These methods can be
called now from the 'validate' object of any xyneo models just like the
database methods from the 'db' object.
- xIsFullname() method was fixed. Now it searches for invalid characters
and can be used to validate hungarian full names too.