FastR Grid: generic Graphics2D device + png, jpeg, and bmp support

...com/oracle/truffle/r/library/fastrGrid/DoSetViewPort.java

.../truffle/r/library/fastrGrid/FastRGridExternalLookup.java

...c/com/oracle/truffle/r/library/fastrGrid/GridContext.java

...com/oracle/truffle/r/library/fastrGrid/GridLinesNode.java

...acle/truffle/r/library/fastrGrid/IgnoredGridExternal.java

...rary/src/com/oracle/truffle/r/library/fastrGrid/Unit.java

...oracle/truffle/r/library/fastrGrid/device/GridDevice.java

...oracle/truffle/r/library/fastrGrid/device/ImageSaver.java

...e/r/library/fastrGrid/device/awt/BufferedImageDevice.java

.../r/library/fastrGrid/device/awt/BufferedJFrameDevice.java

...ffle/r/library/fastrGrid/device/awt/Graphics2DDevice.java

.../truffle/r/library/fastrGrid/device/awt/JFrameDevice.java

.../oracle/truffle/r/library/fastrGrid/grDevices/DevOff.java

...fle/r/library/fastrGrid/grDevices/InitWindowedDevice.java

...le/r/library/fastrGrid/graphics/RGridGraphicsAdapter.java