combination of 8 commits.
piwik: add event tracking

add tests

piwik: fix brackets in test

piwik fix tests

value fallback to revenue

add comma

fix tests

finalize tests
added fix for createdAt and created for group method, along with tests
Merge pull request #446 from segmentio/fix/piwik

 combination of 8 commits.
Merge pull request #449 from segmentio/fix/intercom

added fix for createdAt and created for group method, along with tests