Less cluttered interface

- Less cluttered user interface (based on ideas by Wytze):

  - Sidebar gone.

  - Floating window with the progress indicator and 'run' button.

  - When the loading is done, the progress indicator disappears and the 'run'
    button is shown.

  - Sidebar buttons at the bottom are gone, too.
Placement tweak
Removing striped class if the progressbar is finished
Updated changelog
Removed abbreviation
Merge pull request #3 from lizardsystem/reinout-wytze-animation

Less cluttered interface (based on Wytze's feedback)