Experience upgrade splash screen.

Behaves similarly to the DatabaseUpgradeActivity. You have a
static list of ExperienceUpgrade models that include a "trigger"
version, where when a user upgrades through it a notification
will appear, and there will be a splash explanation screen.

Right now the splash screens are basic and not too configurable,
but that can be reworked as upgrades demand.

Closes #4151

AndroidManifest.xml

@@ -200,6 +200,11 @@
               android:launchMode="singleTask"
               android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"/>
 
+    <activity android:name=".ExperienceUpgradeActivity"
+              android:theme="@style/Theme.AppCompat.Light.NoActionBar"
+              android:launchMode="singleTask"
+              android:configChanges="touchscreen|keyboard|keyboardHidden|orientation|screenLayout|screenSize"/>
+
     <activity android:name=".PassphraseCreateActivity"
               android:label="@string/AndroidManifest__create_passphrase"
               android:windowSoftInputMode="stateUnchanged"
@@ -435,5 +440,12 @@
         </intent-filter>
     </receiver>
 
+    <receiver android:name=".ExperienceUpgradeActivity$AppUpgradeReceiver">
+        <intent-filter>
+            <action android:name="android.intent.action.PACKAGE_REPLACED"/>
+            <data android:scheme="package" />
+        </intent-filter>
+    </receiver>
+
 </application>
 </manifest>