Page specific cache key, unit and functional tests

Only the first cached page was used for all /changes URLs, regardless of page.
Added templates from CWP template to make the module useful standalone outside of CWP.
Added travis CI support. The trigger is already enabled in the SilverStripe Travis account,
so it should start building as soon as we merge.

There's two TODO notes in the test, its a bit unlcear if the /changes endpoint
should contain the original version or not (/allchanges does).