Find examples to convert to tutorials

[choldgraf]

@story645 and @phobson brought up good points that many examples have enough content / topics to really be more in-depth tutorials. I think it's a great idea. What if we use this issue to identify groups of examples that fit this description, and we can open PRs later to improve them.

• colorbars (Convert colorbar_only to tutorial #8561)
• annotations (Consolidate and move examples out of pylab #8266)
  ...

[story645]

Also the style tutorial should likely be updated with the new context manager notation.