pridane serializery pre tag a post
views and routes update

* just fixed CBV - works again
delete works

* confirmation form for delete
* set redirect after object is deleted
create/update process changes

* post_form.html updated
  * shows proper headline
  * redirects to proper target
* save() in Post is not failing, if it is existing entry
update and create

* save() in Post model works fine for insert and update
fixed issue with tag-list

* fixed template tag_list.html
fixed author_list.html template