Stats: display a graph of user scores

[vimark1]

Use a Line chart to display all user's scores, starting from the first one.

See related stats in #78 and #77

[zilehuda]

taking this one @vimark1

[vimark1]

Awesome!

[zilehuda]

@vimark1 check my pull request
#81

[vimark1]

Thanks @zilehuda - have added a comment