feat(vkApi): make "data" and "callback" settings optional
fix(background ajax): use content type "form" for POST data

Send POST data as "application/x-www-form-urlencoded", not as json.

See: http://visionmedia.github.io/superagent/#post-/ put requests
feat(vkApi): add APP_ID field

Add app.vkApi.APP_ID
fix(dislikes): use the new VK host app instead of old ones

Replace old app IDs with app.vkApi.APP_ID

New application was also configured to work with dislikes.
chore(meta): bump version to 0.3.0