Add two proof step to deduce the instantiation of a schematic symbol.

src/main/scala/lisa/kernel/Printer.scala

src/main/scala/lisa/kernel/fol/FormulaDefinitions.scala

src/main/scala/lisa/kernel/fol/TermDefinitions.scala

src/main/scala/lisa/kernel/proof/SCProofChecker.scala

src/main/scala/lisa/kernel/proof/SequentCalculus.scala