cleanup Original/Ogushi/FiFA layout algorithms

[masuhar]

In the source code, there are at least three files that implement layout algorithms (....write the file names here...). Those algorithms should be able to be selected via the Preferences dialog.

1. Currently, the dialog works but we don't understand why.
2. Currently, the dialog can choose either FiFA or Original, but some other algorithms might also be selected.
3. Currently, the implementation seems to use if (selecet == "FiFA") do something else do something eles ... style, which is not so modular. Use classes or other module mechanism.