Integrate w/ Laika 0.19

[armanbilge]

To track the changes relevant to sbt-typelevel-site.

• [ ] https://github.com/planet42/Laika/pull/269
• [ ] https://github.com/planet42/Laika/pull/270
• [ ] https://github.com/planet42/Laika/issues/259
• [ ] https://github.com/planet42/Laika/issues/264
• [ ] https://github.com/planet42/Laika/issues/285
• [ ] https://github.com/planet42/Laika/pull/328

[jenshalm]

I hope this PR (https://github.com/planet42/Laika/pull/328) can convince you to add deprecating the tlRelatedProjects setting to the list above. It was useful when any customization would have required a custom template, but now the Helium API options are more flexible and generic than the this fairly prescriptive setting.

[armanbilge]

Thanks for the heads up, that looks like a nice change!