Fix with of columns, so to avoid switching alignment during scroll

[carlstermannluecke]

The width of the columns (Level, Timestamp, Message) is dynamic and depends on the length of the message (apparently). The problems are:

1. A lot of space is wasted, because the columns for level and timestamp are much wider than needed.
2. The widths and therefore alignments of all columns change during scroll when a longer message appears in / disappears from the scroll window.