Since there is no probability information for users' custom phrases,
they should be stored in a format differs from data.txt. Using the same
format and FastLM to parse user phrases just because of laziness but it
is not the right way.
The pull request adds a new language model class to parse user phrases.
It also update the input method controller to adopt the new user phrase
format.
The reference of the global language models were stored in the class
InputMethodController, however, the global models are global but not a
part of the input method controller, and the input method controller
only use one of the models (McBopomofo/Plain Bopomofo). I guess it
somehow violates SRP and there should be a better place for the global
models.
zonble