Adapted from qwertz DE to match qwertz fr_CH layout.
Added all missing characters with accents needed in French while leaving the most common Swiss German characters as it is on the Swiss layout PC keyboard.
Re-organized some special characters to be in a similar position than the PC layout.
* Add locale fr-CH
The new `layouts` preference replaces three previous preferences:
layout
second_layout
custom_layout
Add a preference migration function, which first migration is to
migrate layouts into the new preference.
The migration must also be called from the SettingsActivity as it might
use a different preference store due to the boot-aware preference copy.
This merges the "Layouts" option with the "Custom layout" option.
A custom layout becomes an item in the "Layouts" list among the other
layouts. It's possible to add several custom layouts.
Selecting the "Custom layout" item in the list opens a second dialog for
entering the layout description.
Layouts are serialized as JSON object and are decoded solely in the
LayoutsPreference class.
Allow items to be of any class instead of strings.
Item serialization and deserialization methods are in a separate class
because they are also used in a static context.
Several non-string keys can have a large label that shouldn't be elided,
for example ctrl, meta, send.
Also, change the cutoff to 3 characters as labels are easily colliding.
The dead-key is replaced by its alternative if there's only one
specified.
Extra keys from every subtypes must be merged together to be able to
make this check.
For each extra key, a list of alternative can be specified. An extra key
won't be added to the keyboard if all its alternatives are already
present on it.
This is useful to avoid having the dead key for an accent and the
accented letters at the same time.
The two layout selection options are replaced by a ListGroupPreference
that allow to enter an arbitrary amount of layouts.
The "switch_second" and "switch_second_back" keys are replaced by
"switch_forward" and "switch_backward", which allow to cycle through the
selected layouts in two directions.
Layouts are changed to place these two key on the space bar.
The backward key is not shown if there's only two layouts.
