automatically resize button and text with window by adding a layout

We choose a vertical layout for the main window and switched the buttons
and texts vertical size policy from fixed to minimum.
add a reset menu item to reset the initial state of the program

We add a menu item "Reset" by clicking into the menu bar in the
designer. In the action editor window we right click on the new action
"Reset" and then "Go to slot..." which opens up a window with all
possible actions. We choose "triggered()" and then fill the code into
the newly created action stub.
add an icon for reset to the toolbar

This way the reset menu item is easier to access.

We first drew an svg image using inkscape. Then we right clicked on the
project and choose "Add new...". In the new window we choose "Qt
resource file" and named it "icons.qrc". We then added the already
existing icon file with "Add existing files...". Now we doubled clicked
the new resource file, added a new prefix and then added the icon.

To add the action to the toolbar we dragged it in the designer from the
action editor to the empty toolbar on top of the window. We then edited
the action in the action editor and selected the icon from the resource
file.