Delay initialization

We want to delay initialization of the `DefaultFijiService` until _after_ the `LegacyService` has initialized (and hence set up ImageJ1 as desired, including patches). But we cannot add a direct dependency on `LegacyService` via the usual `@Parameter` mechanism because that would hose the class loading process. So let's make `DefaultFijiService` initialize itself very late in the game.