Allow different colors definition for timegraph outputs.

Before #442 the horizontal, vertical gridline and text color used where the same. Only one style `lineColor` is defined in the `OutputComponentStyle`. This `lineColor` is propagated to the TimeGraphComponent and TimeAxisComponent. Having different style properties in `OutputComponentStyle` allow to be more selective when configuring the colors.

Please note #442 hard-coded the horizontal and vertical gridline color in `TimeGraphComponent` and with the implementation of this tracker, the hard-coded values can be removed and the new color properties can be used.

Start by tracing OutputComponentStyle into TimeGraphComponent and TimeAxisComponent, focusing on the existing lineColor propagation and the hard-coded gridline colors introduced by #442. Define separate style behavior for horizontal gridlines, vertical gridlines, and text, remove the hard-coded values, and verify that each output can be configured independently.

Written by the indexing model from the issue text.