title: gitignore: Ignore all files in folder hierarchy except one specific filetype
body: <p>I'd like to ignore all files below and in a folder except a specific filetype that could be somewhere in the folders hierarchy:</p>
  
  <p>Example </p>
  
  <pre><code>/Test
  /Test/unknown/folder/structure/below
  </code></pre>
  
  <p>Now I'd like to ignore all files in and below the <code>Test</code> folder except a certain css file named <code>layout.css</code>, e.g.:</p>
  
  <pre><code>/Test/layout.css
  /Test/fileto.ignore
  /Test/another/folder/ig.nore
  /Test/in/a/unknown/folder/layout.css
  /Test/in/a/unknown/folder/ignore.me
  </code></pre>
  
  <p>.gitignore should ignore</p>
  
  <pre><code>/Test/fileto.ignore
  /Test/another/folder/ig.nore
  /Test/in/a/unknown/folder/ignore.me
  </code></pre>
  
  <p>My .gitignore file does not work:</p>
  
  <pre><code>Test/
  !layout.css
  </code></pre>
  
  <p>Any suggestions?</p>