Made ASaxEventRecorder similar to SaxEventRecorder
Fix incorrect error message in <param> when missing "value"
Clean-up unused core test constant
Remove deprecated configuration rules

This removes <contextProperty> and <variable> from Logback configuration
rules. They had been deprecated for <substitutionProperty> and <property>,
respectively.
Add unit tests for Android-related classes

This adds unit tests for code in the ch.qos.logback.*.android packages:

  * ASaxEventRecorder
  * LogcatAppender
  * CommonPathUtil