Crystal structure and ferromagnetic phase transitions in CeCu$_{1-x}$Ge$_{1+x}$ (0.0$\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}}$$x\mathbin{\lower.3ex\hbox{$\buildrel<\over {\smash{\scriptstyle=}\vphantom{_x}}$}} $0.3)