title: Unable to use android.arch.lifecycle:extensions and com.android.support:preference
body: <p>I need to use <code>LifecycleObserver</code> in my app (already existing one).</p>
  
  <p>This's my <code>build.gradle</code> (app):</p>
  
  <pre><code>apply plugin: 'com.android.application'
  
  android {
      compileSdkVersion 27
      defaultConfig {
          applicationId "it.tux.app"
          minSdkVersion 24
          targetSdkVersion 27
          versionCode 1
          versionName "1.0"
          testInstrumentationRunner "android.support.test.runner.AndroidJUnitRunner"
      }
      buildTypes {
          release {
              minifyEnabled false
              proguardFiles getDefaultProguardFile('proguard-android-optimize.txt'), 'proguard-rules.pro'
          }
      }
  }
  
  dependencies {
      implementation fileTree(dir: 'libs', include: ['*.jar'])
      implementation 'android.arch.lifecycle:extensions:1.1.1'
      implementation 'com.android.support:preference-v7:27.1.1'
      implementation 'com.android.support:appcompat-v7:27.1.1'
      implementation 'com.android.support.constraint:constraint-layout:1.1.3'
      implementation "com.android.support:support-core-utils:27.1.1"
      implementation 'com.android.support:design:27.1.1'
      implementation 'com.android.support:support-v13:27.1.1'
      implementation 'io.github.controlwear:virtualjoystick:1.9.2'
      implementation 'com.google.android.gms:play-services-maps:17.0.0'
      implementation 'com.google.code.gson:gson:2.8.5'
      implementation 'com.jjoe64:graphview:4.2.2'
      testImplementation 'junit:junit:4.12'
  }
  </code></pre>
  
  <p>Of course I put also:</p>
  
  <pre><code>allprojects {
      repositories {
          google()
          jcenter()
          maven { url 'https://maven.google.com' }
      }
  }
  </code></pre>
  
  <p>in project <code>build.gradle</code>.</p>
  
  <p>After gradle sync I got an error about incompatibility between <code>com.android.support:preference-v7:27.1.1</code> and <code>androidx.*</code> dependencies.
  If I try to compile things get worse. How can I fix this?</p>