Revert "Revert "Revert "App: only init the data store once per application."""

Even more reverts. :(
After additional testing (based on user reports) it seems like this may
still be causing issues. I find it weird and don't understand why, but
I'm reverting this as a precaution so people aren't affected.

Related to #97

This reverts commit da3ac48bbf.

app/src/main/java/com/etesync/syncadapter/App.kt

@@ -51,7 +51,8 @@ class App : Application() {
      * `@Provides @Singleton`.
      */
     // override onUpgrade to handle migrating to a new version
-    val data = initDataStore()
+    val data: MyEntityDataStore
+        get() = initDataStore()
 
     fun initDataStore(): MyEntityDataStore {
         val source = MyDatabaseSource(this, Models.DEFAULT, 4)