iptsd v2

With this release, the version numbering scheme for iptsd changes. It is now a single number that gets incremented every release, so the next release would be iptsd v3, followed by iptsd v4, and so on. Since we only maintain a single branch, the previously used semantic versioning isn't very useful. And while I tried to differentiate between bugfix and feature releases, it isn't always easy or possible.

• iptsd-check-device is now built without any special instructions to avoid illegal instruction errors on older devices
• iptsd-show now handles window events properly and won't be marked as not responding (@iwanders)
• DFT button signals will only be used if they are from the same group as the position signal (@quo)