Lazy category: methods for cokernel
lazy category: zero object
lazy category: terminal object
lazy category: initial object
lazy category: direct sum
lazy category: coproduct
lazy category: direct product
lazy category: pullback
lazy category: pushout
lazy category: image
Renaming methods (Pushout)

AddInjectionOfCofactorWithGivenPushout
->
AddInjectionOfCofactorOfPushoutWithGivenPushout
lazy category: well-defined sources and ranges
New derivations for IsMonomorphism & IsEpimorphism

Closes #14
Derive morphism to terminal object from ZeroMorphism

and dual statement.

Closes #7
Image

added CoastrictionToImage
Proper implementation of Image