made entry, dataset and chartdata serializable

[jkwiecien]

Made model base objects ChartData, Entry and DataSet serializable hopefully covering the whole model this way

[almic]

Sorry if I'm not getting it, but is this really all that's needed for such a thing to work? I would need to test this before pulling it, and right now I'm working to bring the issue and pull request count down to a manageable number. I'll be back in a day or two and update you.

[trav3711]

Hello! I'm currently trying to serialize an ArrayList of BarEntry objects and I keep getting an error. Is an Entry Serializable?

[hannesa2]

While you wait 7 years for a merge (the last merge was 3 years ago), I merged it here already