Got rid of CompileSession class: this class shouldn't have had any objects, now it is transformed into KotlinToJVMBytecodeCompiler

(JetJavaMirrorMaker still can be returned by PsiPackage.getClasses())

#KT-1771 fixed

 #KT-1645 fixed

re-enabled the Map.Entry key/value properties (not quite sure why they were disabled, tests all seem to work?) and tidied up the sample code for the kdocs

avoid default arguments on groupBy() by having groupByTo() if the caller wishes to specify the Map to group into. Also tidied up the sample code in CollectionTest

Fix test's name

* custom versions
* normalization code moved out of norializer
* hide DESCRIPTOR_TO_DECLARATION (make package local)

* assert runtime implementations from JetStandard* are not loaded
  by JavaDescriptorResolver
* fix wrong @JetMethod in jet.Iterator
* fix jet.Iterator ns was created
* fix incorrect number of functions and tuples in JetStandardClasses
* added TODO about inconsisten Tuple class

 #KT-1763 fixed

 #KT-1757 in progress

 #KT-1755 fixed

JetCoreEnvironment encapsulates a project (in the IDEA sense), so the classpath and sources lie in its area of responsibility