Redesign the property menus, use sub-menus instead of toggles

The toogles are very confusing, one cannot easily see to which
mode one will switch when a toggle is clicked. When the floating panel
is shown, tooltips explain to which mode will switch. But the floating
panel is never shown in Gnome3, so this does not help for Gnome3.

User feedback also shows that many users are confused whether the
currently visible menu entry in case of a toggles shows the state
which is currently used or the state one will switch to when that
toggle is clicked.

For toggles which have more than 2 values, for example the Chinese mode:

    0 means to show simplified Chinese only
    1 means to show traditional Chinese only
    2 means to show all characters but show simplified Chinese first
    3 means to show all characters but show traditional Chinese first
    4 means to show all characters

it is tedious to change from mode 0 to mode 4 for example:

   Open the menu, click on the toggle, menu closes and one has
   changed to mode 1. Repeat 3 more times to get to mode 4.

The new system to use sub-menus instead of toogles also agrees better
with:

https://wiki.gnome.org/AllanDay/IMEGuidelines

> Avoid mutable menu items (menu items whose label changes after it has
> been selected). Instead, consider providing two adjacent menu items
> for the commands. Then make the items sensitive or insensitive as the
> situation demands.
>
> Do not use mutable menu items to toggle a two-state setting (for
> example, Show and Hide). Use a check box or radio buttons instead.

Also included in this commit:

- reset() not needed when switching Chinese mode
Update German translations
Update Chinese .po files
Add a Japanese translation file

I did not translate many messages, I mostly want that file
because I run my desktop in Japanese and want to see whether
the translation system is working correctly or not.
Release v1.9.0