Use boundary to compute axes domain in gridliner

[stefraynaud]

Rationale

Gridliner._axes_domain discretizes the unitary domain to find min/max of longitudes and latitudes.
This discretization makes approximative the estimate if bounds.

This PR directly uses native projection boundary to find min and max.
The PR is quite simple and I may have missed some subtleties.

I didn't updated the figures since alot of them are modified and I'm waiting for feedback.

Implications

Gridlines are properly plotted until the boundary.

Fixes #1443

[stefraynaud]

I think this approach cannot be used alone, since it will never work for polar plot for example.
Instead, it but to used to make the base algo more robust.

[stefraynaud]

Now it works well with the best of the two algo.

[dopplershift]

Could you add the image as a test?

[QuLogic]

This may need a rebase to fix CI.

[greglucas]

It looks like you've brought some duplicate commits into this. Can you try to rebase onto master instead of merging master into this branch? I'm not sure why Appveyor failed on the gridliner image tests, but Travis didn't. Maybe it will fix itself with a rerun of the CI...

[stefraynaud]

@greglucas how to proceed with this rebasing?

[greglucas]

I think you have to delete the commits through an interactive rebase, or at least that's how I've done it when things get out of sync between branches.

1. checkout master and fetch/pull the latest master commits from upstream
2. checkout this branch
3. git rebase -i master

That should give you a list of all the commits to choose from and then just keep the ones you want and delete the others. Probably just keeping all of your commits and removing all the merges/other people's commits from the list.

[CLAassistant]

Thank you for your submission! We really appreciate it. Like many open source projects, we ask that you sign our Contributor License Agreement before we can accept your contribution.
_{You have signed the CLA already but the status is still pending? Let us recheck it.}