Release v0.19.0

[devotaaabel]

Release checklist @devotaaabel

• Run through testapp/demo app and test all activities
• Change version name to 0.19.0 in gradle.properties
• Publish 0.19.0 artifact to Maven Central
• Change version name back to 0.20.0-SNAPSHOT
• Update CHANGELOG.md
• Tag v0.19.0 in GitHub

Post-release @langsmith

• Update README.md
• Update constants.js file in android-docs repo
• Generate navigation and navigation-ui javadocs and add to android-docs repo
• Update https://www.mapbox.com/help/android-navigation-sdk/
  • @colleenmcginnis should be good on this one 👍
• Update config files in /help repo after tutorial (☝️) update is finished.

/cc: @mapbox/navigation

[langsmith]

All done on my end @devotaaabel 🎉