wiki pages: use names instead of ids in urls.

Switching to using wiki names in URLs instead of IDs:

* https://danbooru.donami.us/wiki_pages/vocaloid
* https://danbooru.donami.us/wiki_pages/hatsune_miku

ID numbers can still be used, but they redirect to the name instead:

* https://danbooru.donami.us/wiki_pages/11 (redirects to /wiki_pages/touhou).

Numeric tags are prefixed with '~' to distinguish them from IDs:

* https://danbooru.donami.us/wiki_pages/2019 (the wiki with id 2019)
* https://danbooru.donami.us/wiki_pages/~2019 (the wiki for the tag named 2019)

The tag names 'new' and 'search' are disallowed to prevent conflicts
with existing routes:

* https://danbooru.donami.us/wiki_pages/new
* https://danbooru.donami.us/wiki_pages/search

app/logical/tag_name_validator.rb

@@ -25,6 +25,8 @@ class TagNameValidator < ActiveModel::EachValidator
       record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
     when /\A(#{Tag.categories.regexp}):(.+)\z/i
       record.errors[attribute] << "'#{value}' cannot begin with '#{$1}:'"
+    when "new", "search"
+      record.errors[attribute] << "'#{value}' is a reserved name and cannot be used"
     when /\A(.+)_\(cosplay\)\z/i
       tag_name = TagAlias.to_aliased([$1]).first
       tag = Tag.find_by_name(tag_name)