Change color of clicked point only. Show pop up at position of clicked point.

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What steps will reproduce the problem?
1.Create a line chart graph.
2.Click on the graph.
3.Point color needs to change. Using onTouch, we could not get the exact 
location and varies for every touch.

What is the expected output? What do you see instead?
Add a method to renderer, to make the color to clicked point different. Method 
to show the popup at the point clicked.

Please provide a source code snippet that we can use to replicate the
issue.

What version of the product binary library are you using?
1.2.0

Please provide any additional information below.

Original issue reported on code.google.com by kavurusa...@gmail.com on 30 Dec 2014 at 11:27