ggplotly: separate facet columns by <br>

[alyst]

Currently ggplotly uses , to separate facet_grid() columns.
The PR changes that to <br> to make it more compatible with ggplot (every column on its own line).
It would also help with overlapping row/column long labels.

[cpsievert]

Thanks @alyst, this looks promising.

Would you mind bringing this up-to-date with master? With ae6b073, the tests should no longer report false positive test errors, and we can see a more informative test reporter.

It would also be awesome if you could write a test with multiple line breaks to demonstrate the difference!

[alyst]

@cpsievert Do you mean PR #471 ? There it's also about line breaks :) I've just rebased that one and updated the "group" tests. I can rebase this PR as well.

[cpsievert]

Thanks! I'm afraid #471 might not get merged. I'm working on a big rewrite locally right now (which will fix this problem) and I'll start a pull request in the next few days.