Bug "Login inconsistant across devices" fixed

This pull request matches with the bug "Login inconsistant across devices".
https://github.com/SMILEConsortium/smile_teacher_android/issues/11

![12439e56-ca25-11e2-99d4-fb90df9db104](https://f.cloud.github.com/assets/3521208/786652/dfc8b568-eabf-11e2-8a47-b32773389e16.jpg)

I adapted the layouts of activity_flow.xml, login.xml, and save.xml for mobile format.
I added a missing tag <View android:id="@+id/view_separator_score" ... ... /> in students.xml.
I also added a handler in LoginActivity to manage messages outside onCreate() method (because the app crashed).
I finally tried to adapt the views for prepared question and the dashboard but I think everything should be resized or adapted in mobile format.