Add support for line traces classification

[allyoucanmap]

Description

We should introduce the possibility to classify line traces in a similar way as we are doing with bar chart. The main use case we are focusing are time series. As an example we could have a dataset including at least following attributes:

• an identifier or category e.g. id
• a date/time attribute e.g. year
• a value to represent on the y axis e.g. population

In this type of dataset structure we would like to use the year on the x axis, population on the y axis and use the classification style to group by the id to get multiple traces for each identifier.

Requirements:

• A new style classification type for the line trace

What kind of improvement you want to add? (check one with "x", remove the others)

• Minor changes to existing features

Other useful information

Datasets for testing:

• NYPD Complaint Data Historic data see main chart in https://github.com/geosolutions-it/events-tracker