RFR: 8244657: ChoiceBox/ToolBarSkin: misbehavior on switching skin

[Jeanette Winzenburg]

Both skins have similar misbehavior when switching skins

- memory leak due to a manually added but not removed change listener
- NPE when modifying items after skin switch due to a not removed listener to the control's items

Fixed in both (for details see the issue). Added SkinCleanupTest for simple testing of per-control side-effects,
removed both skins from memory test exclusion list: failing before and passing after fix.

-------------

Commit messages:
 - 8244657: ChoiceBox/ToolBarSkin: misbehavior on switching skin

Changes: https://git.openjdk.java.net/jfx/pull/238/files
 Webrev: https://webrevs.openjdk.java.net/jfx/238/webrev.00
  Issue: https://bugs.openjdk.java.net/browse/JDK-8244657
  Stats: 158 lines in 4 files changed: 150 ins; 3 del; 5 mod
  Patch: https://git.openjdk.java.net/jfx/pull/238.diff
  Fetch: git fetch https://git.openjdk.java.net/jfx pull/238/head:pull/238

PR: https://git.openjdk.java.net/jfx/pull/238