Implement missing event handlers in the default Slack::RealTime::Stores::Store

[dblock]

There're still a number of unimplemented event handlers in https://github.com/dblock/slack-ruby-client/blob/master/lib/slack/real_time/stores/store.rb to be implemented.

[stevendaniels]

That file is missing. Is there a more up to date list of realtime api events available?

[dblock]

Slack documents them here: https://api.slack.com/events. Maybe the README could use a link?

[dblock]

The internal event handling was refactored on HEAD, I've edited this issue to describe what I really want out of it (aka implement the missing event handlers in the default local store).