Added autofocus.

Added autofocus for login as well as every add/edit pages.
Added preview capabilities for posts.

Added preview for the posts writting. It's simply a JS script that
takes the content from the title and content textareas and sets it
as the html content of two other containers. It refreshes on key
presses.
Only displays categories if there are posts for it in Archives.
Added a dropdown menu to the title bar for narrow displays
Removed bootstrap css and fonts and replaced it with CDN.
Added limit to get_posts and get_posts_list.