Implement basic support for LET expression & predicate

src/main/java/de/tlc4b/analysis/MachineContext.java

src/main/java/de/tlc4b/analysis/Renamer.java

src/main/java/de/tlc4b/analysis/Typechecker.java

...n/java/de/tlc4b/analysis/UnsupportedConstructsFinder.java

...ava/de/tlc4b/analysis/typerestriction/TypeRestrictor.java

src/main/java/de/tlc4b/prettyprint/TLAPrinter.java

...est/java/de/tlc4b/analysis/UnsupportedConstructsTest.java

src/test/java/de/tlc4b/prettyprint/OperationsTest.java