Move flag checking for minimum required version to manifest

This is still not the best solution, ideally we would save this to some kind
of configuration file that we can use for dev/prod etc. Also, this solution
doesn't work with iOS or web

android/app/src/main/AndroidManifest.xml

@@ -26,6 +26,7 @@
         android:icon="@mipmap/ic_launcher">
 
         <meta-data android:name="wger.api_key" android:value="${WGER_API_KEY}" />
+        <meta-data android:name="wger.check_min_app_version" android:value="true" />
 
         <activity
             android:name=".MainActivity"