Stop using the old `aether` and `eclipse-aether` libraries, who's code is now part of `maven-resolver`, under the `org.eclipse` package. The old libraries are very abandoned, to the point that their websites have gone missing. They depend on some scarily broken libraries, which is a problem for distros like Debian.
Tests green. Only non-find-and-replace changes is to add some properties:
- `<javaVersion>7` as `maven-resolver` uses 7 and otherwise enforcer gets angry, and
- `<maven.version>3.5.2`, as pre-3.5 maven used aether for other reasons, so it still ends up polluting the tree.