Use getter setter in classes in bmp.h

[Ank1taS]

Classes of bmp.h contain all public attributes. As we implement C++, it is better to keep all attributes private and have public getters and setters.

revert back to #8

[H1manshu21]

Getters and Setters should be used for classes in bmp.h so that it will follow the OOPs paradigm. @Ank1taS @chandrakant100 @HembramBeta777 @sabyasachi07