General: Make UI suitable for small screen sizes and enable split view

[terlan98]

Split view would be useful for scenarios where the user want's to see an earlier assessment while assessing a new submission. Enabling it is quite straightforward: remove the tick from the 'Requires full screen` checkbox in project target settings (general tab):

Nevertheless, Themis is made for the iPad, so it does not work well in small screen sizes. Splitting the screen leads to a result similar to running the app on an iPhone. That's why the app needs to be adjusted for small screen sizes first.