Spaces after markdown links should escape the link creation

[brianlovin]

Overall it's really challenging to stop typing a link after it's already been created. See this demo:

https://www.dropbox.com/s/1tcqkss1gav5u6h/link-formatting.mov?dl=0

Basically it's not clear how to stop typing a link.

A couple proposed changes:

• If we have an inline toolbar, a user can just select text to linkify/unlinkify it. Solves the problem.
• If a user is typing a markdown link, don't auto-format it after the closing ) parentheses. Dropbox Paper does this - just keep the user's formatting because they know what they are doing with Markdown.
• Re-expand a link to the markdown syntax when it is clicked or selected.