plugin: set a default value for the activeLanguage ("en"), to have a good initialization from the start

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Keyboard settings: fix wrong signal emitted for keyPressFeedback setting

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>
Word prediction: fix generation of presage database files.

It no longer puts output files directly in the source tree, and nicely copy them during install step.

Signed-off-by: Christophe Chapuis <chris.chapuis@gmail.com>