Add support for calculating ReplayGain on unidentified clusters

[emersonrp]

This commit allows unidentified clusters in the "left pane" to be run through the plugin and have their ReplayGain calculated. Previously the plugin could only be used on identified tracks and albums in the "right pane."

With this commit, one or more clusters can be scanned as albums, and the album and track ReplayGain added to the files. There is no change to the existing / previous functionality for identified albums and tracks.

[emersonrp]

I see that Codacy is saying that the "calculate_replaygain" method is too complex. I think it's not appreciably more complex than it used to be, though it of course is a bit longer. I can refactor this to get around the Codacy issue, but that expands the scope of the change, and has more possible impact on the existing functionality. Happy to do the right thing, be it refactoring or just living with the Codacy issue, as y'all see fit. Thanks.

[emersonrp]

Also I have just noticed that this is actually an open issue, #344

[phw]

Thanks a lot, this is very helpful.

I see that Codacy is saying that the "calculate_replaygain" method is too complex. I think it's not appreciably more complex than it used to be, though it of course is a bit longer. I can refactor this to get around the Codacy issue, but that expands the scope of the change, and has more possible impact on the existing functionality.

Yes, I think the codacy check is a bit too strict here. It calculates complexity by considering the different possible code paths in some way. And because your change introduces several "if" conditions it now got above the threshold.

We could address this by splitting the function calculate_replaygain further up into separate functions, e.g. extracting building the file list or applying the metadata to files, but I don't think it does help much for the code readability in this case.

I think we can raise the codacy complexity limit or ignore the complaint for this case.

Otherwise the code looks fine to me. I'll test run this and then I think we can merge this change.

Also I have just noticed that this is actually an open issue, #344

Yes, exactly, this is the fix for this issue. As mentioned it was initially left out intentionally, but has been requested frequently since then. Great you provided this fix.

[phw]

Everything working as expected. Thanks again for this contribution