HG-279: changed logic for next and previous buttons and fixed issue with comments on one page
HG-279: cleaner fix for next button for comments on a page with too little comments
fixed unit test for ArticleCommentsModel
added checking buttons state to ArticleComments component tests
CR changes: make it more consistent
Merge pull request #308 from Wikia/HG-279

HG-279 Fix bug with displayed "Next page" button in ArticleComments component