Fix CapsLock handling in EvdevKeyboard plugin

CapsLock was incorrectly handled in EvdevKeyboard, which led non-letter
keys to be masked with Qt::ShiftModifier. The default builtin keymap
is modified to have IsLetter flags for correct keys.

Task-number: QTBUG-32560

Change-Id: I561bbad7bcffe1f4c4bbed7bf72106b689e57fe0
Reviewed-by: Andy Nichols <andy.nichols@digia.com>
Add how to create a udev rule for the evdev plugins

Change-Id: Icd7a192701958673fe216f40ddab710f5f63a8b8
Reviewed-by: Paul Olav Tvete <paul.tvete@digia.com>
Reviewed-by: Andy Nichols <andy.nichols@digia.com>