0.6.3 Fix WeakListener regression

As described in Issue #47, there was (another) regression concerning the usage of WeakListener.

This has been fixed.

Full Changelog: v0.6.1...v0.6.3

0.6.1 Bugfix for removeCheck

This bugfix release fixes Validator.removeCheck(...). Existing decorations had not been removed from the scene.

0.6.0 - Allow manipulation of GraphicDecorations

0.6.0 allows an application to access the decoration node of an existing GraphicDecoration object, thus allowing to customize the GraphicDecoration created by DefaultDecoration.createGraphicDecoration(...).

0.5.1 - WeakListeners

0.5.1 changes ValidatorFX so that it uses weak listeners. This prevents memory leaks in the case where a Check depends on a property whose lifetime is longer than the Check / Validator object.
Issues involved: #38 and #39.