Pressing arrow keys on BigDecimalField should repeat increment/decrement until mouse is released

This is equivalent to pull request #67 that was included into the 2.2 branch.

- Not sure you will be interested in this change. But.. What this change accomplishes is supports is adding support for auto repeat of the up/down arrow action of the BigDecimal field. Holding the mouse button down on the up arrow will increment the field repeatedly on a timer until the mouse is released. Holding the mouse button down on the down arrow will decrement the field repeatedly on a timer until the mouse is released. This behavior is helpful when the user wants to increment/decrement the value in the field quickly. Also, it makes the mouse actions a bit more consistent with the keyboard, as the up/down arrows on the keyboard exhibit the same behavior.