Corrects a bug in Chart.js Module and some other issues

[cauemello]

This PR corrects:
1- a bug occurring in chart when the reset button was pressed.
2- the ticks visualization on x-axis when chart has too many values => #77
3- the datacollector data with the corresponding model step * => #268

• In order to work properly, we must collect data after defining the initial state of the model (step 0) and after each step. So, we must collect data as the last line of model init and after each schedule.step().

[coveralls]

Coverage remained the same at 82.911% when pulling 872a83b on cauemello:master into 67f14ab on projectmesa:master.

[TaylorMutch]

While I think it is by and large appropriate to use => notation for declaring functions, since we are not using any sort of build process, it is best for the time being to use the long-form declaration of functions.

chart.data.datasets.forEach(function(dataset) {
    while (dataset.data.length) {
        dataset.data.pop();
    }
})

[coveralls]

Coverage remained the same at 82.911% when pulling 9ab0397 on cauemello:master into 67f14ab on projectmesa:master.

[TaylorMutch]

The duplicated collect initial data comments seem unnecessary given that we're calling datacollector.collect.

[TaylorMutch]

@cauemello See my comment about your comments. I will try to test your changes soon!

[coveralls]

Coverage remained the same at 82.911% when pulling 1df1ff6 on cauemello:master into 67f14ab on projectmesa:master.

[TaylorMutch]

@cauemello I will look over this tonight and see if we can get this taken care of.

[cauemello]

Hi @TaylorMutch , is this PR out of Mesa 0.8.3 release? Did you find any problem with the code?

[TaylorMutch]

Looks good, sorry for the long wait.