With the addition of the language support module, ReaderDictionary
tries to use modules registered with the UI instance, but the
FileManager doesn't provide key-based registration of its UI modules.
In order to allow the same code to be used by both FileManager and
Reader seamlessly, copy the :registerPlugin() method from Reader and use
it with FileManager. This will ensure any other hidden assumptions about
UI module registration are handled properly.
Signed-off-by: Aleksa Sarai <cyphar@cyphar.com>