[HiDPI] Unify icon metrics

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
[HiDPI] Resolution-independent DiveEventItem icon sizes

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>
[HiDPI] Resolution-indepent dive pictures

Signed-off-by: Giuseppe Bilotta <giuseppe.bilotta@gmail.com>