Bump version to 0.1.90

Open the development of the new version.
Replace QTermWidget with yat and switch from QtWidgets to QtQuick

Long live QML!
Configuration header

Introduce a configuration header. At the moment it only has version
information.
Copy yat's QML files and make a new main file

Copy yat's QML code here to easily use it and add a new main file using
QtQuick Controls.
Reuse yat's main.qml

Reuse it for now.