adding free points from CindyScript does not invoke the prover

[kortenkamp]

When adding elements using the createpoint(…) function, the prover does not need to be invoked. However, it was, leading to a quadratic runtime when adding n points. I tried to fix this by invoking addElementNoProof instead of addElement, but this still had quadratic runtime as the conjectures comparing the new element to all other elements are created in the addElementNoProof code.

This pull request changes the behaviour of addElementNoProof to match its name – conjectures are only created when the prover is invoked, and also uses addElementNoProof for the createpoint(…) function.

An example illustrating the now instant creation of 999 elements has been added as well, the Stellenwerttafel. Add a point in the first column and then drag it to the rightmost column to create 999 elements. This took about 5-15 seconds, depending on the computer/tablet you used, and is now immediate.

This closes #894.

[kortenkamp]

Merging this as an emergency fix – Stellenwerttafel is being used today at a lecture in Dresden.