Add selection example

[JHawk]

This is a composite example adding 3 different mouse selection methods to <regular-table> - row, column and area. Each literate example has a single function to add its respective behavior - addRowMouseSelection(), addColumnMouseSelection() and addAreaMouseSelection(). Finally, I've added a composite example that applies each of the behaviors into a single example seen in the gif attached.

Also includes an example use of area selection in implementing copy/cut, paste using the keyboard with addAreaClipboard().

[texodus]

Thanks for the PR!

Very, very cool feature, great test coverage also. Let's make sure to add this to the gallery!