Lmms: Implement directory watching / auto-refresh for file browser

[Wallacoloo]

Under linux, there exists a tool called inotify which allows an application to watch a directory and be notified whenever something about it changes (new file added/deleted, existing file modified, etc).

A natural way to use such a tool is to monitor all the open folders in the file browser and update the UI in real-time as the folders are modified, saving the user from having to manually refresh the directory view, or forgetting to.

inotify is linux only, but a quick search reveals these equivalent cross-platform tools (though I know little of their reputation/usability):

• simplefilewatcher (Win/Mac/Linux, poll-based, MIT license)
• libfswatch (Win/Mac/Linux/FreeBSD, callback-based, GPLv3 license)

The latter option looks to be better all-around (more actively developed, doesn't require calling "update()" on a regular basis, and it supports slightly more backends), except for the less-permissive license, but LMMS is licensed under the GPL anyway ( :-1: ) so that's pretty much moot.

[lukas-w]

Note for anyone wanting to try their luck: This should be relatively easy to implement using QFileSystemWatcher.

[Cruwal]

I'll work on this!

[lukas-w]

@Cruwal Any progress on this? Let us know if you need help.