Nit changes to HomeActivity/Fragment (#219)

app/src/main/java/org/oppia/app/home/HomeActivity.kt

@@ -6,11 +6,11 @@ import javax.inject.Inject
 
 /** The central activity for all users entering the app. */
 class HomeActivity : InjectableAppCompatActivity() {
-  @Inject lateinit var homeActivityController: HomeActivityController
+  @Inject lateinit var homeActivityPresenter: HomeActivityPresenter
 
   override fun onCreate(savedInstanceState: Bundle?) {
     super.onCreate(savedInstanceState)
     activityComponent.inject(this)
-    homeActivityController.handleOnCreate()
+    homeActivityPresenter.handleOnCreate()
   }
 }

app/src/main/java/org/oppia/app/home/HomeActivityPresenter.kt

@@ -0,0 +1,24 @@
+package org.oppia.app.home
+
+import androidx.appcompat.app.AppCompatActivity
+import org.oppia.app.R
+import org.oppia.app.activity.ActivityScope
+import javax.inject.Inject
+
+/** The controller for [HomeActivity]. */
+@ActivityScope
+class HomeActivityPresenter @Inject constructor(private val activity: AppCompatActivity) {
+  fun handleOnCreate() {
+    activity.setContentView(R.layout.home_activity)
+    if (getHomeFragment() == null) {
+      activity.supportFragmentManager.beginTransaction().add(
+        R.id.home_fragment_placeholder,
+        HomeFragment()
+      ).commitNow()
+    }
+  }
+
+  private fun getHomeFragment(): HomeFragment? {
+    return activity.supportFragmentManager.findFragmentById(R.id.home_fragment_placeholder) as HomeFragment?
+  }
+}

app/src/main/java/org/oppia/app/home/HomeFragment.kt

@@ -10,14 +10,14 @@ import javax.inject.Inject
 
 /** Fragment that contains an introduction to the app. */
 class HomeFragment : InjectableFragment() {
-  @Inject lateinit var homeFragmentController: HomeFragmentController
+  @Inject lateinit var homeFragmentPresenter: HomeFragmentPresenter
 
   override fun onAttach(context: Context?) {
     super.onAttach(context)
     fragmentComponent.inject(this)
   }
 
   override fun onCreateView(inflater: LayoutInflater, container: ViewGroup?, savedInstanceState: Bundle?): View? {
-    return homeFragmentController.handleCreateView(inflater, container)
+    return homeFragmentPresenter.handleCreateView(inflater, container)
   }
 }

app/src/main/java/org/oppia/app/home/HomeFragmentController.kt → app/src/main/java/org/oppia/app/home/HomeFragmentPresenter.kt

@@ -12,7 +12,7 @@ import javax.inject.Inject
 
 /** The controller for [HomeFragment]. */
 @FragmentScope
-class HomeFragmentController @Inject constructor(
+class HomeFragmentPresenter @Inject constructor(
   private val fragment: Fragment,
   private val viewModelProvider: ViewModelProvider<UserAppHistoryViewModel>,
   private val userAppHistoryController: UserAppHistoryController