Add some more features and bugfixes

[flxholle]

I've created a fork of this app for the moodle-instance mebis, used by many schools in bavaria (https://github.com/asdoi/MebisApp/). In this fork I added some more features like:

• Biometric app lock
• Dialog if login data is wrong
• Splash screen
• Log-in button actions
• Remove nested scroll view

For a full list see the release section: https://github.com/asdoi/MebisApp/releases If you'd like I can integrate some of the features in your app, but I do not have the time to create a pull request for every feature, I would just make a big one and if you do not like some changes I would simply remove them.