Added Choose expression

src/main/scala/inox/ast/DSL.scala

src/main/scala/inox/ast/ExprOps.scala

src/main/scala/inox/ast/Expressions.scala

src/main/scala/inox/ast/Extractors.scala

src/main/scala/inox/ast/Printers.scala

src/main/scala/inox/ast/TreeOps.scala

src/main/scala/inox/evaluators/RecursiveEvaluator.scala

src/main/scala/inox/evaluators/SolvingEvaluator.scala

...main/scala/inox/solvers/unrolling/TemplateGenerator.scala