Use plotly titles over annotations when appropriate.

[BRONSOLO]

Currently we are using annotations for all titles because of the flexibility with positioning.

[chriddyp]

We used annotations instead of titles to have titles that were centered perfectly on graphs that have an off-centered colorbar. We've since updated Plotly to have evenly spaced margins for plots with colorbars and so the titles should now be centered.

[BRONSOLO]

Addressed in #56