title: Different Manifest for mutliple flavors with Gradle
body: <p>I have this situation : 4 flavor, i must have 8 build totally, 4 app declaring an Accessibility in the manifest and 4 not.
  I have found as only solution declare 2 buildTypes in manifest, so that I can create a sourceSets for the buildType, specifing manifest src. But in this way I have under build</p>
  
  <ol>
  <li>Accessibility</li>
  <li>No accessibility</li>
  <li>debug</li>
  <li>release</li>
  </ol>
  
  <p>So now i can't have a accessibility <strong>debug</strong> to test, so I had to create other 2 buildTypes specifying debuggable true. Final situation is </p>
  
  <ol>
  <li>Accessibility</li>
  <li>Accessibility debug</li>
  <li>No accessibility</li>
  <li>No accessibility debug</li>
  <li>debug</li>
  <li>release</li>
  </ol>
  
  <p>Those are only  <strong>buildTypes</strong> , but i also have 4 flavor so my build variants are 24.</p>
  
  <p>This sucks basically. There's no way to declare two sourceSets used by default debug and release ?</p>
  
  <p><strong>REQUIRMENTS</strong></p>
  
  <pre><code>flavor1/accessibilty
  flavor1/no accessibilty
  flavor2/accessibilty
  flavor2/no accessibilty
  ecc..
  </code></pre>
  
  <p><strong>FIRST IMPLEMENTATION</strong></p>
  
  <pre><code> buildTypes {
      noaccesibiltyDebug {
          minifyEnabled false
          debuggable true
      }
      accessibilityDebug {
          minifyEnabled false
          debuggable true
      }
      noaccessibilty {
          minifyEnabled true
          debuggable false
          proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
      accessibility {
          minifyEnabled true
          debuggable false
          proguardFiles getDefaultProguardFile('proguard-android.txt'), 'proguard-rules.pro'
      }
  }
  sourceSets {
      noaccessibiltyDebug {
          manifest.srcFile('/src/main/AndroidManifest.xml')
      }
      accessibilityDebug {
          manifest.srcFile('/src/main/accessibility/AndroidManifest.xml')
      }
      noaccessibilty {
          manifest.srcFile('/src/main/AndroidManifest.xml')
      }
      accessibility {
          manifest.srcFile('/src/main/accessibility/AndroidManifest.xml')
      }
  }
  </code></pre>
  
  <p><strong>RESULT</strong></p>
  
  <pre><code>build/output/apk/accessibilty
                  /noaccessibilty
                  /accessibiltyDebug
                  /noaccessibiltyRelease   
                  /debug &lt;- **********useless**********
                  /release &lt;- **********useless**********
  </code></pre>