Add ability to track exceptions

[alexanderdean]

Resources:

• http://www.javaworld.com/article/2072391/the-surprisingly-simple-stacktraceelement.html
• https://github.com/yeller/yeller_java/blob/master/src/com/yellerapp/client/ExceptionFormatter.java
• https://github.com/getsentry/raven-java#same-frame-as-enclosing-exception
• https://github.com/airbrake/airbrake-java/blob/master/src/main/java/airbrake/Backtrace.java

[mscwilson]

Other Snowplow trackers e.g. JavaScript tracker has a "track error" event type, using the schema iglu:com.snowplowanalytics.snowplow/application_error/jsonschema/1-0-1.

This would not be automatic error tracking, but could be configured.