Catch UnsupportedOperationExceptions from getDesktop.
Add a little more protection in getElementAt because Apples' LAF
sometimes returns -1.
Merge pull request #128 from openrocket/issue-118

Catch UnsupportedOperationExceptions from getDesktop.
Improve refreshing the decal model by doing it whenever the underlying
appearance changes.  This allows for "From file" to work correctly as
well.
Merge pull request #129 from kruland2607/fixdecaldropdown

Fix for issue #116