Add mixture list view with pagination. Closes #12.

* Add mixture list template.
* Add URL configuration for mixture list.
* Add mixture list implementation.
* Add modal size setting.
* Add link to mixture list.
* Fix header page name.
* Change thumbnail size in mixture detail.
* Add setting for max items in mixture list view.
* Add mixin to filter by pagination.
* Add pagination implementation.
Merge branch 'issue#12-Add_view_all_mixtures' into develop