Lot's of changes in authors & tags

* Added a TagListView and a AuthorListView which show all Tags/Authors
* Renamed AuthorEntriesPlugin to AuthorsPlugin and massive Cleanup
* Added archive-day view
*  **Furthermore, this fixes:** https://github.com/aldryn/aldryn-blog/issues/33 & https://github.com/aldryn/aldryn-blog/issues/32