views: update seo title and description of post index page.

Change the title of the post index page to look like this:

    "Danbooru: Anime Image Board" (for the front page)
    "Kantai Collection Art | Danbooru" (for a tag search)

Change the meta description of the front page to look like this:

    Danbooru is the original anime image 'booru. Find over 3.75 million
    anime pictures categorized by over 100 million tags.

Change the meta description for a tag search to look like this:

    Find over 37,168 Azur Lane images on Danbooru. Azur Lane (碧蓝航线)
    (벽람항로) is a Chinese shipgirl-themed side-scrolling shoot 'em up
    mobile game developed by Shanghai Manjuu and Xiamen Yongshi...

config/danbooru_default_config.rb

@@ -25,10 +25,6 @@ module Danbooru
       "Danbooru"
     end
 
-    def description
-      "Find good anime art fast"
-    end
-
     # The canonical hostname of the site.
     def hostname
       Socket.gethostname