Types (#166)

* Starting a layer of abstraction.

* swrdgv

* sedgf

* ONgoing work. FOL structure mostly implemented, substitutions ongoing.

* continued

* further changes

* LisaObject has a self type being self

* More improvements on substitution

* More work

* multivar substitution

* improvements to MapProofTest

* finished fol, need to do prooflib

* started work on prooflib, cut plenty unused code in Library.scala

* more work on substitutions

* updated WithTheorems

* finished BasicSteptactics and substitutions

* more corrections of tactics using unifier

* fixed F and K imports

* finished PrrofHelpers and definitions. Definitions possibly not final

* Done most of the simpleDeducedSteps

* ongoing work on types

* added doc in Common.scala

* more doc, some simplification

* more doc and simplification of unneeded parts

* fixed some export issues. Commented some tests. translation left for the future.

* remove some debug code

* add missing files

* continue F integration. FInished with Set theory library files, now doing CommonTactics.scala (part is Dario's work).

* simplifier remaining

* renaming and mroe compatibility

* more adaptations

* merge build.sbt

* fixing

* transforming unification to Front

* weird issues with match types and dotty

* Compiles..? Need to simplify use of Arity in formula labels now. Finger crossed.

* add missing files

* still compiles

* Term**0 |-> Term

* Does not compile (dotty crash). Possibly due to covariant schematic labels.

* Labels are contravariant

* Weird "inherits conflicting instances of non-variant base trait LisaObject"

* structure seems to work; Constant extends ConstantFunctionSymbol[0], issue with case class (has to reimplement).

* back to the "common super type with case classes" structure

* finished predicates, compiles. Connector left

* Finished datastructure. TODO: Underlyings, Arity, uncomment asFront

* Compiles, checked arity and underlyings (mostly)

* Rehabilited asFront. Next stop, Substitution.

* porting unificationUtils

* half of unificationUtils done. Need to make Common even closer structure to kernel (variableFormula extends PredicateFormula)

* progress through unification

* compiles, progressing

* safe for reset

* only applySubst remaining.
Note: given
```scala
val s: Seq[(Variable, Term)]
```
`s.toMap` crashes dotty. Instead, do `Map(s*)`.

* Substitution done, everything compiles.

* rehabilited commented function

* utils tests compiles and pass.

* Finished setTheorzLibrary, close to finish OLPropositionalSolver

* Quantifiers.scala work, completed BasicProofTactic, implemented printing of terms and formulas

* progress on compilation and run of SetTheory.scala

* ordinals1 works

* Everything works, even example package. Some tests are still commentated. Simplified a couple proofs.

* Small improvements

* Ready for demo

* scalafix, scalafmt

* git add

* Removed unused option in build.sbt, run scalafixAll and scalafmtAll on lisa-examples, add a newline in build.properties