DeferredImageDescriptor and DerivedImageDescriptor keep the original
descriptor / supplier refrences and can't be cached, because that opens
a door for memory leaks in 3rd party code.

Also added missing license header for LazyResourceManager, that was
missing in original patch for bug 576740.

Change-Id: I0196f11b94c3d8d6be635dcdecfff0d1b23d60bc
Signed-off-by: Andrey Loskutov <loskutov@gmx.de>
Reviewed-on: https://git.eclipse.org/r/c/platform/eclipse.platform.ui/+/187221
Reviewed-by: Sebastian Zarnekow <sebastian.zarnekow@gmail.com>
Reviewed-by: Jörg Kubitz <jkubitz-eclipse@gmx.de>
Tested-by: Platform Bot <platform-bot@eclipse.org>