List block: Add keyboard support for list indenting and outdenting

[DevinWalker]

Issue Overview

Currently when using the list block element you cannot indent lists using the keyboard shortcut (⌘ + ]) or tab. As well, you can not easily outdent using (⌘+ [) or (shift + tab). This means increased time to make lists that are more than one hierarchy.

I believe adding this would help improve the usability. Currently you can use (⌘ + b) to bold and same for italics, why not also for list indenting?

Notes:
This functionality is referenced here: #1552

[afercia]

Worth noting using the Tab key for indentation breaks keyboard navigation through blocks.

[DevinWalker]

Noted. But tabbing is not really working as currently should for all blocks currently:

I would prefer (⌘+ [) rather than the tabbing for indenting lists.

[BoardJames]

One other thing that needs to be considered is that '[' and ']' are not on all keyboards. I'm told that the locales 'fr', 'nl', 'sv', 'ru', 'de', 'es' and 'it' do not have those keys. Apparently on textbox.io the square brackets, "meta+]" for indent and "meta+[" for outdent, are used on most locales and "meta+m" / "meta+shift+m" is used for the ones which don't have the square brackets.

I will put in a pull request with those key bindings.

[afercia]

Right, for example on an Italian keyboard layout [ and ] can be typed only pressing Alt+è and Alt++.