Add a glossary entry for "device" to make changing the definition
easy and link the first occurrence of "device" in a topic to it,
where applicable.

Change-Id: Ia1b8b669b0000eea47d6a7b9860d3329d93a4395
Reviewed-by: Vikas Pachdha <vikas.pachdha@qt.io>
Reviewed-by: Tarja Sundqvist <tarja.sundqvist@qt.io>
Reviewed-by: Topi Reiniö <topi.reinio@qt.io>
Reviewed-by: Leena Miettinen <riitta-leena.miettinen@qt.io>