Create wrapper package for fcitx with plugins.

This creates a wrapper package for fcitx so that plugins can be enabled by the user.  This is based on the wrapper package for pidgin-with-plugins.

By using this wrapper instead of the fcitx package itself, it will be possible for the user to enable/disable plugins.

This is an improvement over #4713 that just makes a wrapper package with the plugins instead of creating an entire new package that must be compiled.  This also closes the issue #4550.