Revert "Only let one card viewing activity exist at a time"

This prevented the editing of cards, as the same activity
was used for viewing and editing, but the viewing "instance"
was calling finish(). It is simpler to remove the singleTop
option.

This reverts commit 4e02252b75.

app/src/main/AndroidManifest.xml

@@ -36,7 +36,6 @@
             android:name=".LoyaltyCardViewActivity"
             android:theme="@style/AppTheme.NoActionBar"
             android:configChanges="orientation|screenSize"
-            android:launchMode="singleTop"
             android:windowSoftInputMode="stateHidden"/>
         <activity
             android:name=".BarcodeSelectorActivity"