In the timelines work packages which only have a start date or only an end date are displayed as black blocks which span more than the original length.
They should instead have a gradual transition.
When only the start date is set, the color of the start date should be stronger and then get weaker.
When only the end date is set, the color of the end date should be stronger and the time up to it should be weaker.

**Expected**
They should be displayed Begin of the insertionproperly.

**Screenshot**
End of the insertion