DefaultOptionsService: remove obsolete hack

Now that options are lazily registered with the object service itself,
we no longer need to force lazy instantiation explicitly.
DefaultPlatformService: simpler platform selection

Now that platforms are lazily registered with the object service itself,
we no longer need to lean on the plugin service directly to query
platforms. We can just use our singletons directly.
ImageCalculator: remove obsolete hack

Now that calculator ops are lazily registered with the object service
itself, we no longer need to force lazy instantiation explicitly.
Merge branch 'lazy-singletons'

This branch removes obsolete hacks and workarounds from the codebase,
relating to the fact that lazily initialized services did not add
their objects to the object service until their actual first use.

Now, with SciJava Common 2.4.0, we can register a callback to add
objects which do not yet exist to the object service, such that it will
generate them on demand. This avoids the very surprising situation of
certain objects (notably SingletonPlugin instances from each
SingletonService) not being available from the object service.