marker single tap listener

[armancodv]

PR Checklist:

• [*] I have tested this extensively and it does not break any existing behavior.
• [*] I have added/updated examples and tests for any new behavior.
• [*] If this is a significant change, an issue has already been created where the problem / solution was discussed: [N/A, or add link to issue here]
  

PR Description

This MR adds a new method to the gesture listeners for tapping on the marker view.
issue #144

It doesn't remove anything, it just adds a new listener to OnChartGestureListener.

It could be helpful for cases that users need to customize data by tapping on the marker.

[Paget96]

I really like this library and using it in my apps, I would like to call people to continue with this awesome thing. I have forked the repo and started working on it! So I am ready as well to accept pull requests, I'll notify other people from here as well!
Would be more than happy if we continue with this awesome project.

Code is full kotlin now!

Make your pull requests here:
https://github.com/Paget96/MPAndroidChart