Move ugoira_player.js into application.js.

Fixes an issue with the ugoira player not working on Safebooru due to
this error:

    Asset filtered out and will not be served: add
    `Rails.application.config.assets.precompile += %w( ugoira_player.js)`
    to `config/initializers/assets.rb` and restart your server

app/assets/javascripts/application.js

@@ -4,6 +4,7 @@
 //= require jquery.timeout.js
 //= require jquery-ui-autocomplete-custom.js
 //= require jquery.storageapi.js
+//= require ugoira_player.js
 //= require rails.js
 //= require common.js
 //= require_tree .

app/views/posts/partials/show/_ugoira_original.html.erb

@@ -37,7 +37,6 @@
 </div>
 
 <% content_for(:html_header) do %>
-  <%= javascript_include_tag "ugoira_player" %>
   <script type="text/javascript">
     Danbooru.Ugoira = {};