Wrap LogStash::Event with Yarder::Event

To start with let us wrap the Logstash::Event inside a
Yarder::Event class. This gives us the possibility of making
changes without havting to monkey-path LogStash::Event
Refactoring into Yarder::Event

Start moving methods into the Yarder::Event model
Merge branch 'no_rack_events'
Make Yarder::ActiveRecord::LogSubScriber non-request friendly

ActiveRecord quite often logs things outside of a request /
response cycle (For example, background jobs). This is a quick
and dirty patch to make sure that ActiveRecord does not explode
if this happens.