Add a reset Button

[RiedleroD]

when pressed, the button should

• stop the current algorithm (if any)
  by pressing the start/stop button if it's on stop
• delete all current buckets
• create one new bucket

This button will be useful for several purposes:

• resetting if weird bugs are encountered by the user
• resetting if the item count changes (see #5)
• sorting the list without having to wait for an algorithm to sort it
• filling the hole in the left top corner of the UI