move RContext into separate package

...gine/src/com/oracle/truffle/r/engine/RContextFactory.java

...fle.r.engine/src/com/oracle/truffle/r/engine/REngine.java

...rc/com/oracle/truffle/r/engine/RRuntimeASTAccessImpl.java

...ine/src/com/oracle/truffle/r/engine/TruffleRLanguage.java

...ine/src/com/oracle/truffle/r/engine/repl/RREPLServer.java

...le/truffle/r/engine/repl/debug/RDebugSupportProvider.java

...om/oracle/truffle/r/engine/shell/JLineConsoleHandler.java

...ngine/src/com/oracle/truffle/r/engine/shell/RCommand.java

...m/oracle/truffle/r/engine/shell/StringConsoleHandler.java

.../src/com/oracle/truffle/r/library/fastr/FastRContext.java

...c/com/oracle/truffle/r/library/fastr/FastRStackTrace.java

...src/com/oracle/truffle/r/library/fastr/InteropExport.java

...src/com/oracle/truffle/r/library/fastr/InteropImport.java

.../src/com/oracle/truffle/r/library/graphics/RGraphics.java

...oracle/truffle/r/library/methods/MethodsListDispatch.java

....library/src/com/oracle/truffle/r/library/utils/Menu.java

...c/com/oracle/truffle/r/nodes/builtin/RBuiltinPackage.java

.../com/oracle/truffle/r/nodes/builtin/RBuiltinPackages.java

...oracle/truffle/r/nodes/builtin/base/BrowserFunctions.java

...ltin/src/com/oracle/truffle/r/nodes/builtin/base/Cat.java