ui: better progress bars

[Suor]

Currently we have progress bars for each individual file, which is not helpful when we have many of them. Furthermore when using several threads - a common case - they just fill up a screen, with no indication of where we are.

So I propose switch to using one progress bar for a single mass operation. There was a question from @efiop: how do we show all the filenames that are being processed? I would say we can only show single file taking longest so far like:

[========                             ] 17% big-dataset.csv + 7 other files

Or we can list them in a second line after the progress bar, but I don't think it matters too much.

Another thing that we should probably approach simultaneously is how we code that. Now we pass flags like no_progress_bar, sometimes deep enough to make code ugly. I suggest using global progress bar variable, like logger instances so we won't need pass anything. To guarantee that scope won't leek we can use context managers:

with progress(name=..., total=...):
    # ...
    progress.update(value)  # This may come in some nested func
    # ...

Or wrap iterables:

for item in progress(seq, name=..., total=...):
    # process item

To hide progress bars in all called code, without any flags passing:

with progress.hide():
    # ...

[shcheklein]

Can we somehow show a progress for the whole operation (vs per file)? For example count the total files size and show progress by bytes transferred, also would be great to see total speed per second and other stats.

+1 on refactoring the code.

[ghost]

Hello, @casperdcl ! Not directly related to progress bar but I would like to hear your input on this one #2329 (also related to UI)