text: Title: Color choice for multivariate timeseries
  Body: **Is your feature request related to a current problem? Please describe.**
  Currently, it is not possible to choose the color of each component in a multivariate timeserie.  It is only possible to choose a color for all componenents of the timeserie.
  
  **Describe proposed solution**
  Enable the user to provide a list of colors (that must be a long as the number of components in the timeserie) to set the colors of the components in the plot.
  
  **Describe potential alternatives**
  Alternatively, one could provide the name of a colormap and darts would automatically sample colors from the colormap for the components of the timeserie. 
  