Add *-containing-point functions and testOnly cmd.

- edd-package-containing-point finds the surrounding package like
ensime-package-containing-point but takes into account multiple package
declarations.

- edd-class-or-module-containing-point does the same for top-level
  class/object

- edd-fqn-containing-point gives the fully-qualified class/object name

- test-only invokes the above to run sbt testOnly <class>