Better progress feedback for file operations

[mherrmann]

Currently, fman prints what files it is currently operating on in the status bar. It would be nicer to have (say) a progress bar. But should be unobtrusive/non-blocking. A user pointed out that time estimates are probably impossible to get right, so best to avoid them entirely.

[mherrmann]

Further requirements / nice to haves:

• Any plugin should be able to display progress feedback via fman's API.
• It would be nice if the user were also able to pause / abort the long running operations (if the plugin supports it).
• The progress feedback should make it possible to display errors specific to that operation.

[mherrmann]

@joshas suggested maybe taking Filezilla as an inspiration for what the progress feedback could look like.

[webdesus]

Maybe better make core plugin? I think in a future fman have many plugins for copy use ftp protocol, smb, and etc. I think if we will be bet common interface for control copy operations, all future plugins created for file operations, can use this common UI. What do you think about it?