adds snowplow event plugin

	new file:   vendor/assets/javascripts/plinth/plugins/tbg-snowplow.js.coffee
documents removeData function

	modified:   vendor/assets/javascripts/plinth/plugins/tbg-snowplow.js.coffee
doc fix

	modified:   vendor/assets/javascripts/plinth/plugins/tbg-snowplow.js.coffee
Fixing naming error from GA to SP
Merge pull request #66 from thebeansgroup/feature/snowplow-events

Feature/snowplow events