Fixing some unicode and Italian translation issues

[albertosottile]

I am experimenting with files with non-ASCII characters in their name or path, and I have found some issues in the current version. In the following, there is a detailed list of what I found so far and how I fixed it. I am using this PR to keep track of these bugs and changes, since I am currently in the process of finding and debugging some of them.

Unicode support

• file properties (name, size, duration) are not loaded if filepath contains non-ASCII characters.
• (macOS) drag-and-drop of files with non-ASCII characters in their path does not open the file.
• (macOS) drag-and-drop of filepaths with non-ASCII characters on the shared playlist does not load the file.
• File names with non-ASCII characters make ConsoleUI crash and Syncplay unusable
• (macOS) File names with non-ASCII characters are always seen as different in VLC and mpv, with both GraphicsUI and ConsoleUI
• • (macOS) No differences other than "name" are shown in VLC and mpv if filename contains a non-ASCII character in both GraphicsUI and ConsoleUI
• (VLC) "file differences: name" is initially triggered when a file with non-ASCII characters in its name is opened from VLC, then the player drops this difference, but the OSD does not update. (These may be more bugs, actually).

Italian translation

• (VLC) Readiness status is not shown in the OSD if there are any file differences.

Other (not a bug probably):

• File differences are logged in the Notifications only when remote users change their files, not when the local user changes it. This is true also for ConsoleUI messages. Player's OSD and GraphicsUI are always up-to-date.

[Et0h]

I'm hoping to release 1.5.3 soon to fix an issue with HTTPS on the Windows builds. Is this okay to merge or does it need more tweaks to resolve the outstanding issues?

[Et0h]

Tested on Windows and everything in patch seems fine. As otherwise discussed the file difference issue still needs resolving for macOS.