Detect language of text

[osma]

A possible enhancement for the Finto AI user interface would be to detect the language of input text. This would be easy to implement if the corresponding functionality is added to the Annif REST API: see NatLibFi/Annif#631

How best to add this feature to the UI needs a bit more thought. I can think of two approaches:

1. Make this functionality completely separate from the subject indexing. Basically, a button (or other widget) that the user clicks on and then the UI shows the detected language.
2. Integrate with the subject indexing functionality. For example, first detect the language, then narrow down the available projects based on the language (example: if the text is detected as English, show only projects intended for English language).