#638 Use new Tycho and Maven features.

• Changes
  • Automatically include all required references in the update site.
  • Ensure all artifacts in the update site have sources. This includes unlisted product (headless) features and their bundles.
  • Use set-parent-version instead of set-version, for less work.
  • Configure tycho.pomless.aggregator.names globally in the project. No more need for mvn_escet either.
  • Remove update site per-platform archive extensions configuration. This configuration is now the default.
• Probably best to review per commit.

Closes #638 (closed)