Add support for skolem variables

[iduartgomez]

Add support for existential variables in logic sentences.

[iduartgomez]

Right now there is support of a sort of existential variable in ind. conditional sentences, in the form of:

given entity A, if there is such A for which condition p holds then q(A)

here A is reified, is not purely existential, and the consequence q is also reified.

However what should be the goal is to have existential variables that allow for the following sort of 2nd order effects:

1) given entity A, if p then q(A)
2) given such A if q then r 

Here q should not need to be reified, just proven true by the conditional of the first sentence and would transitively translate to the 2nd sentence.