Add title to vertical chart layout about cmapplot

[matthewstern]

@dlcomeaux, concurrently with this work I'd like to overhaul the finalize vignette.

I propose rearranging the sections as follows, and making substantive changes as per the parentheticals:

• Basic implementation
  • Finalizing
  • Exporting
• Customization
  • Top-level position adjustments (remove debug mode, remove reference to legend_shift)
  • Exporting a graph with no title
  • Title and caption formatting
• Advanced customization
  • Using debug mode
  • Overriding plot constants
  • Shifting the legend (new, brief section explaining legend_shift)
  • Many, many margins (consider adding second slide to describe margins in a title_width = 0 setting)

What do you think? I'm happy to work on this concurrently/after your commits.

[dlcomeaux]

That sounds like a good structure to me, @matthewstern