Re-levelization: move non-docs content, rename content→docs

For better URLs, the content folder has been renamed 'docs' and all
other files have been moved up a level. Also, non-docs images have been
moved to the static folder at the top level where they belong.

Many relative paths had to be fixed to make this work.

@i18n/ja/docs/_snippets/interactive-tutorials/connect-step.md

@@ -0,0 +1,17 @@
+<!-- Interactive tutorials are hard-coded to Testnet for now due to Redocly 
+     limitations. They'll be replaced with new-style tutorials next anyway.
+     Localized step names don't currently work due to problems with unicode
+     in regexes. -->
+
+{% interactive-block label=default($label, "Connect") steps=$frontmatter.steps %}
+
+<button id="connect-button" class="btn btn-primary" data-wsurl="wss://s.altnet.rippletest.net:51233" data-explorer="https://testnet.xrpl.org">Testnetに接続する</button>
+<div>
+  <strong>接続ステータス：</strong>
+  <span id="connection-status">接続されていません</span>
+
+  {% loading-icon /%}
+
+</div>
+
+{% /interactive-block %}

@i18n/ja/docs/_snippets/interactive-tutorials/generate-step.md

@@ -0,0 +1,9 @@
+{% interactive-block label=default($label, "Generate") steps=$frontmatter.steps %}
+
+<button id="generate-creds-button" class="btn btn-primary" data-fauceturl="https://faucet.altnet.rippletest.net/accounts">Testnetの暗号鍵を作成する</button>
+{% loading-icon message="暗号鍵を作成しています…" /%}
+<div class="output-area"></div>
+
+{% /interactive-block %}
+
+**注意:** Rippleは[TestnetとDevnet](../../concepts/networks-and-servers/parallel-networks.md)をテストの目的でのみ運用しており、その状態とすべての残高を定期的にリセットしています。予防措置として、Testnet、DevnetとMainnetで同じアドレスを使用**しない**ことをお勧めします。

@i18n/ja/docs/_snippets/interactive-tutorials/wait-step.md

@@ -0,0 +1,23 @@
+{% interactive-block label=default($label, "Wait") steps=$frontmatter.steps %}
+
+<table class="wait-step" data-explorerurl="https://testnet.xrpl.org">
+  <tr>
+    <th>トランザクションのID:</th>
+    <td class="waiting-for-tx">(無）</td>
+  <tr>
+    <th>最新の検証レジャーインデックス：</th>
+    <td class="validated-ledger-version">接続されていません</td>
+  </tr>
+  <tr>
+    <th>送信時のレジャーインデックス：</th>
+    <td class="earliest-ledger-version">（まだ送信されません）</td>
+  </tr>
+  <tr>
+    <th>トランザクションの<code>LastLedgerSequence</code>:</th>
+    <td class="lastledgersequence">(準備されません）</td>
+  </tr>
+  <tr class="tx-validation-status">
+  </tr>
+</table>
+
+{% /interactive-block %}