Convert logback.xml to Groovy

This fixes the issue where Logback would generate a
catalina.base_IS_UNDEFINED directory if Tomcat wasn't running. This
would happen, e.g., in unit tests.
Delete ReportAppender

We haven't used it in years (it's been broken). It also doesn't
actually log reports.
Merge pull request #24 from gabegorelick/logback-groovy

Logback groovy