feat(ajax): make same-origin requests in page context

Because some ajax requests need correct cookies and Opera 12
(possibly Firefox too) doesn't pass them when making requests from
background script (it has a different context with a different "document"
and with disabled cookies), we have to split ajax handling:
same-origin requests - in ordinary target window with injected scripts,
cross-origin requests - in background context.

- move uri.js and handle-ajax.litcoffee to source/
- use them in ajax module for same-origin requests
- update background scripts accordingly
- update tests for ajax module

This commit contains cat power.
fix(dislike): make like widget requests in page context

This finally closes #83.
fix(vkApi): add "name" attribute to iframe equal to "id"

This closes #84.