Clean up unused / removed pages & images

- Delete folders for new pages that are handled by templates w/ no
  markdown source
- Fully remove "Use Cases", leaving redirects for deleted pages.
    - Move certain pages to new areas & remove Use Case markup
- Add "Contribute Code to the XRP Ledger" draft page
- Fix image paths in some Japanese-translated pages

content/tutorials/manage-the-rippled-server/stand-alone-mode/advance-the-ledger-in-stand-alone-mode.md

@@ -23,7 +23,7 @@ Whenever `rippled` closes a ledger, it reorders the transactions according to a
     - [server_info method][]
     - [`rippled` Commandline Usage](commandline-usage.html)
 - **Use Cases:**
-    - [Contribute Code to `rippled`](contribute-code-to-rippled.html)
+    - [Contribute Code to the XRP Ledger](contribute-code.html)
 
 <!--{# common link defs #}-->
 {% include '_snippets/rippled-api-links.md' %}

content/tutorials/manage-the-rippled-server/stand-alone-mode/load-a-saved-ledger-in-stand-alone-mode.ja.md

@@ -74,7 +74,7 @@ rippled ledger_accept --conf=/path/to/rippled.cfg
     - [server_infoメソッド][]
     - [`rippled`コマンドラインの使用](commandline-usage.html)
 - **ユースケース:**
-    - [`rippled`へのコードの提供](contribute-code-to-rippled.html)
+    - [XRP Ledgerへのコードの提供](contribute-code.html)
 
 <!--{# common link defs #}-->
 {% include '_snippets/rippled-api-links.md' %}

content/tutorials/manage-the-rippled-server/stand-alone-mode/load-a-saved-ledger-in-stand-alone-mode.md

@@ -75,7 +75,7 @@ rippled ledger_accept --conf=/path/to/rippled.cfg
     - [server_info method][]
     - [`rippled` Commandline Usage](commandline-usage.html)
 - **Use Cases:**
-    - [Contribute Code to `rippled`](contribute-code-to-rippled.html)
+    - [Contribute Code to the XRP Ledger](contribute-code.html)
 
 <!--{# common link defs #}-->
 {% include '_snippets/rippled-api-links.md' %}

content/tutorials/manage-the-rippled-server/stand-alone-mode/start-a-new-genesis-ledger-in-stand-alone-mode.md

@@ -35,7 +35,7 @@ By default, a new genesis ledger has no [amendments](amendments.html) enabled. I
     - [server_info method][]
     - [`rippled` Commandline Usage](commandline-usage.html)
 - **Use Cases:**
-    - [Contribute Code to `rippled`](contribute-code-to-rippled.html)
+    - [Contribute Code to the XRP Ledger](contribute-code-to-rippled.html)
 
 <!--{# common link defs #}-->
 {% include '_snippets/rippled-api-links.md' %}