All wxPG_FILE_xxx attributes are used only in wxFileProperty to set respective internal data members and don't have to be stored in the property's attribute store.
By moving the code to display file selector dialog from wxPGFileDialogAdapter to wxFileProperty we can encapsulate the operation of showing the dialog because all required parameters are stored in the corresponding data members and there is no need to use call generic GetAttribute() function to retrieve them. This also helps in making wxFileProperty attributes built-ones in the future.
This attribute is used only internally in wxFileProperty so it can be considered as a built-in attribute which value can be stored in the local data member and not in the property's attribute store.
OnValidationFailure() in derived class wxEnumProperty has the same implementation (empty body) as the implementation in the base class wxPGProperty so overriding this function in derived class is not necessary.
No real changes, just clean up sources by removing trailing spaces from
all the non-generated files.
This should hopefully avoid future commits mixing significant changes
with insignificant whitespace ones.
