Switch back from Sisu to Plexus

Previous stable line (0.4.x) used Plexus Container Default, but it was
switched to Sisu because I thought that maybe I could use JSR-330
instead of Plexus to simplify code, but the switch broke previously
working code.

It turns out that Sisu is not entirely compatible with Plexus (it
shares loggers between components and has different semantics when
looking up component maps).

Besides that Plexus stack traces are more readable and explain why
particular component could not be injected.  Sisu just gives cryptic
Guice error messages.
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