Pagination

Resolves #15 
Latest demo: http://x2.srijn.net:8080/demo/index.html
Things left to be done:
- [x] Get value of "number of comments to be shown by default" from config
- [x] Top-level and nested `max-comments`
- [x] Correct the value of total number of comments for the url (shown in `#isso-thread > h4`)
- [x] Show all comments on limit/nested_limit = inf
- [x] i18n for the text on "Show More" button
- [ ] Testing on 100s of comments or more
- [x] Add tests
- [x] Docs