Reuse Grid.__init__ in ImageGrid.__init__.

[anntzer]

ImageGrid.__init__ differs from Grid.__init__ by some defaults which
can be passed to the superclass, and by additionally constructing the
colorbar axes. This needs to be pushed into _update_locators which
isn't optimal but still better than duplicating the entire
Grid.__init__.

PR Summary

PR Checklist

• Has Pytest style unit tests
• Code is Flake 8 compliant
• New features are documented, with examples if plot related
• Documentation is sphinx and numpydoc compliant
• Added an entry to doc/users/next_whats_new/ if major new feature (follow instructions in README.rst there)
• Documented in doc/api/api_changes.rst if API changed in a backward-incompatible way

[timhoffm]

Initializing the colorbar in _update_locators() is unexpected.

Can you make a separate method (something like _update_extra_ax, name up for improvement) for updating the colorbar. The method is empty in Grid. IMHO this is better than doing unrelated stuff in _update_locators.

Alternatively, you could find a more general name instead of _update_locators.

BTW: Is it _update_locators or rather _init_locators()? Currently this is only called during setup; and I think it's not feasible to use this method anywhere again later (currently it is not).

[anntzer]

I just renamed it to _init_locators, as that's what it really is.

[timhoffm]

👍 for renaming.