BEM.I18N: Use modules. Closes #59

Quite ugly but working.

Works the same as in `bem-bl` for `i18n.html` tech and via `modules.require(['i-bem__i18n'])` for `browser.js` and `node.js`. In templates `BEM.I18N` syntax is left for backward compatibility but it doesn't pollute global scope in browser or node.js bundle. Still I'm not sure it's a good idea to keep it like that.

@narqo @dfilatov @veged