The numeric layout and the optional right hand side numpad are modified
to show the digits belonging to the script used in the current layout.
The numpads are still defined as it was before. The digits are changed
in `modify_numpad` if needed.
`gen_layouts.py` lists the layouts in `res/xml` and generate the
`pref_layout_values` and `pref_layout_entries` arrays into
`res/values/layouts.xml`.
These arrays are hard to maintain as the order has to match, which is
fragile.
This relies on every layouts having a `name` attribute.
