Better names for SolverFactory and fixed bug in quantifiers

...in/scala/leon/invariant/templateSolvers/CegisSolver.scala

...la/leon/invariant/templateSolvers/FarkasLemmaSolver.scala

...riant/templateSolvers/UniversalQuantificationSolver.scala

src/main/scala/leon/invariant/util/Minimizer.scala

src/main/scala/leon/invariant/util/SolverUtil.scala

src/main/scala/leon/solvers/SolverFactory.scala

...ala/leon/solvers/combinators/PortfolioSolverFactory.scala

src/main/scala/leon/solvers/combinators/SolverPool.scala

...n/scala/leon/solvers/isabelle/IsabelleSolverFactory.scala

.../scala/leon/solvers/unrolling/QuantificationManager.scala

...scala/leon/integration/purescala/SimplifyPathsSuite.scala

...t/scala/leon/integration/solvers/TimeoutSolverSuite.scala

src/test/scala/leon/unit/solvers/SolverPoolSuite.scala