title: Firebase Unresolved Reference
body: <p>I have implemented Firebase database by included assistant. 
  It added to my gradle dependencies <code>implementation 'com.google.firebase:firebase-database:16.0.1:15.0.0'</code></p>
  
  <p>after that, I couldnt build the procject (solution was to change impelentation into kapt)</p>
  
  <p>My gradle looks like:</p>
  
  <pre><code>dependencies {
          kapt 'com.google.firebase:firebase-database:16.0.1:15.0.0'
          implementation fileTree(dir: 'libs', include: ['*.jar'])
          implementation "org.jetbrains.kotlin:kotlin-stdlib-jdk7:$kotlin_version"
          implementation 'com.android.support:appcompat-v7:28.0.0'
          implementation 'com.android.support.constraint:constraint-layout:1.1.3'
          testImplementation 'junit:junit:4.12'
          androidTestImplementation 'com.android.support.test:runner:1.0.2'
          androidTestImplementation 'com.android.support.test.espresso:espresso-core:3.0.2'
          implementation 'com.android.support:design:28.0.0'
      }
  </code></pre>
  
  <p>Then, I needed to retreive a instance of my database</p>
  
  <pre><code>class AppActivity : AppCompatActivity() {
  
      val manager = supportFragmentManager
  
  
      var database = FirebaseDatabase.getInstance()
  </code></pre>
  
  <p>and its error,  <em>unresolved reference: FirebaseDatabase</em></p>
  
  <p>I have tried to deal with it, but it seems its beyond me. </p>
  
  <p>Guys, any idea what is the reason ? </p>