Avoid generation of separate header files for Handle classes

In order to minimize amount of files in OCCT include folder, it is proposed to avoid generation of Handle_*.hxx files for CDL, generating definition of class and its Handle in the same header file. This will allow to decrease number of header files in include folder by ~ 3.500.

Naturally, in some cases when several classes refer to each other it can be feasible to keep definition of the Handle in separate header. This should be made on a case-by-case basis. For examples, see packages LDOM, TObj, OpenGl.