Simplify SCIFIO class hierarchy

This change eliminates the distinction between a SCIFIOComponent versus
a SCIFIOPlugin, in favor of everything being a SCIFIOPlugin.
Furthermore, it eliminates the HasSCIFIO and HasLog interfaces in favor
of using SciJava Common's built-in parameter injection mechanism.

By using the parameter injection mechanism, creation of a SCIFIO context
will "fail fast" with an IllegalArgumentException when a service depends
on another required service, rather than receiving an NPE later when
first attempting to access that service via the SCIFIO gateway.

For convenience, the log() method still exists as an API method of
SCIFIOPlugin, since it is a pain to inject the LogService into
absolutely every implementing class. ;-)