Switch from ibus-anthy to Mozc

Originally created by @mercedes508 on #16719 (Redmine)

Hey received a bug report from a japanese user, complaining about our current input method for japanese.

Here are a few reason why it would be better to switch to fcitx-mozc:

• the accuracy of the conversion of Anthy to Kanji is so bad that the amount of
  kanji that can be converted is small, so it is useless
• most japanese users use mozc

And in order to use this piece of software one has to reboot Tails after installing, so adding it through additional software doesn’t do the trick.

Feature Branch: feature/16719-ibus-mozc

Related issues

• Has duplicate #17389 (closed)