step extension docs

[kahboom]

This PR is to add documentation for creating a custom view, or Step Extension. There was already a "Custom Views" post that I've essentially just updated to include details of the Step Extension API.

NOTE: This is NOT documentation for the API, this is just for creating a Step Extension. The next PR would include details about the methods exposed, but this was a requirement for that.

I also added some other nice changes in:

• Added a markdown render hook for all remote links (those that don't begin with /) to be opened in a new tab.
• Fixed a lot of formatting for syntax highlighting. Now we can actually take advantage of code line number highlighting for certain code types. See screenshots below.
• Overrode the footer so we could make changes to it. I changed the URL to just show the handle for social media stuff.
• Removed unused references to Baidu, Google Maps plugin, etc.
• Changed typography a bit to use 'Lato' as the base font, as it's more readable.

Screenshots

Code Syntax Inline (before)

Changes

I also updated old posts that were not using code blocks, since they won't use the styling. Sometimes the inline styling is fine for a short piece of code, but not for a block. See the difference here:

With highlights:

Footer:

relates to https://github.com/KaotoIO/kaoto-ui/issues/214

[kahboom]

Thanks @Delawen , though for some reason the website isn't being updated?

[Delawen]

There is some syntax error:

https://github.com/KaotoIO/kaoto.io/runs/6826513234?check_suite_focus=true