Add titles to all figures and generally improve all notebooks about bqplot

[dmadeka]

• Advanced Plotting
• Animations
• Axis Properties
• Bars
• Basic Plotting
• Boxplot
• Candles
• FlexLine
• GridHeatMap
• Hist
• Interaction Layer
• Label
• Lines
• Map
• Mark Interactions
• Market Map
• Pie
• Plotting Dates
• Pyplot
• Scatter

[sebasgil]

It would be really nice to show how to add x_labels and y_labels in the Pyplot notebook, as well.
In matplotlib it's as easy as declaring

plt.xlabel('string')

whereas the bqplot documentation on pyplot.plot of

If a scale labeled 'x' is required
        for that mark, options['x'] contains optional keyword arguments for the
        constructor of the corresponding axis type.

is cryptic at best.
This would be much appreciated, thanks!

[ssunkara1]

Thanks @sebasgil for reporting this issue. I raised another issue #474 for this so that it is easier to track.