No Album or Photo shown on failed Login

[ramack]

Describe the bug and how to reproduce On starting the app no album or photo is shown in case the login fails.

Expected behavior

• if the login fails (e. g. because the credentials on the server have been changed) for an existing account the login activity shall pop up again with a message, that the login failed. Today we have only a logcat error because in MainActivity.java:109 we just log the exception.

Together with #88 we should show the reason. If network is completely down a dedicated popup shall be shown without the LoginActivity.

[ramack]

As this is a rare use case we can shift it to next release I guess.