update modebar docs

[jdamiba]

The purpose of this PR is twofold:

First, to update some of the language around modebar configuration to make more explicit what options users have to add or remove icons.

• [x] delete old examples
• [x] write new examples

Second, to bring this doc page in line with other pages in terms of having example figures generated inline rather than using embedded codepens.

• [x] remove plot_url front-matter to inline chart
• [x] make sure all figures render appropriately

Thanks @Mahdis-z for pointing this out!

[nicolaskruchten]

:dancer: once we address the "always" comment