refs #4996 trying to ignore content impressions in live api, not sure if that works
refs #4996 use content type in case it was a standalone content impression request which was not performed along an outlink or download or ...
refs #4996 do not return any impression or interaction in live.getVisitorDetails as it would not be accurate anyway. For instance a download or outlink can be an interaction as well when tracked together etc
refs #4996 fix tests
refs #4996 some more tests
Merge pull request #6249 from piwik/4996_content_live_api

More tests for content tracking