Support for tablet Wacom Intuos Medium with Bluetooth (CTL-6100WL)

Summary:
This patch adds support for the tablet Wacom Intuos Medium USB and Bluetooth, model CTL-6100WL (former Bamboo series).
Without this patch, I could not get button 4 (mapped to button 8) to work.

Reviewers: valeriymalov

Reviewed By: valeriymalov

Differential Revision: https://phabricator.kde.org/D21833