Allow setting legend names when multiple series values are used in an Indicator

[zlpatel]

Expected Behavior

There should be a way to specify meaningful legend names when multiple series values are used in a single Indicator

Actual Behavior

Currently, you can only specify single name for Indicator. But there are cases where you need to plot multiple data series in a single Indicator and it's important to label them for easy identification.

Currently, There's an option to specify list of colors (one for each data series). I think if we allow passing list of legend names (as a separate parameter) that would be great.

Additional info

[zlpatel]

After my code fix it looks like this:

[zlpatel]

@kernc could you mark this as an enhancement?