Long file name displayed in a single line in the file widget

Thanks for reporting and working on this @chmez!

I think that the solution which will work with all possible filenames would be better, as mentioned in #13. What are the cons of using word-break: break-all;? It could be even less "intrusive" change in comparision with adding a new checkbox to the file field configuration.

human-readable file names (words separated by spaces) which converts by Drupal (replace spaces by underscores).

Drupal 7 does not have such conversion in the core - do you meant the Transliteration module? We cannot assume that sites will have this module installed. If you upload a file with spaces on vanilla D7 core to the file field, then nothing is changed and the filename is kept as it is.