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();

[kevintanhongann]

if there are no conflicts with the base branch, please merge.

[ginkoblongata]

Looks good, I have one item to point out:

--> "First Mouse click will focus component before allowing it to be dragged"

I disagree that this detail should be the mechanism.

It is a matter of opinion I suppose. I think this happens in a couple of different ways on the various well known desktops.

The behavior that I strongly favor is that of basically "mouse click brings focus to component and start of dragging has begun".
Otherwise the user has to click again for the dragging when that activity is non destructive.