Patch issue#655 - SplitPanel Enhancements / Fixes

[Orbisman]

See Issue #655 for details.

• Added keystroke handing for UP/DOWN/LEFT/RIGHT ARROW keys.
• Moved resizing code to private function
• First Mouse click will focus component before allowing it to be dragged
• Used same handleKeystroke() layout as table to be be consistent
• Added call to invalidate() at the end of the resize() function to fix the mouse dragging issue.
• When resizing, use the area width/height when resizing components
  Note: Updated SplitPanelTest to add additional Splits with Multiline Textbox to show how the components where not expanding

Testing requires the mouse capture turned on in the TestBase class, ie.
Screen screen = new TestTerminalFactory(args).setMouseCaptureMode(MouseCaptureMode.CLICK_AUTODETECT).createScreen();