Added population counters for selected types

[f4str]

fixes #645

Displays counter in parentheses next to selected type. Literal count of all tracks in track list grouped by type. When the type is unchecked, the counter disappears. Counter updates automatically as the confidence filter slider is changed.

Still need some tests on performance and efficiency.

[subdavis]

• Remove unnecessary null check
• Maybe try lodash groupby for an even more concise implementation.

[subdavis]

BTW, nice job figuring out how all this stuff works. track.getType and the context and stuff.

[BryonLewis]

I know it's tight on space in that location, but I'm wondering if we can standardize the location of the count number. I don't know if at the front is the best or if a new 'column' to the right works better? Just so it's easier to scroll down and take a quick look at counts easily.

[subdavis]

Flexbox spacer, maybe?

[subdavis]

@f4str pointed out that the edit button is already in that space. Let's try it like this first?

[BryonLewis]

@f4str pointed out that the edit button is already in that space. Let's try it like this first?

Yeah I knew the edit button was there that's why I was saying we were tight for space as is. I'm good with trying it as is.

[f4str]

Another thing we can try is aligning the count right underneath the gear. The edit button is aligned right underneath the delete button. However, I think it looks kind of weird having a number floating on the right like that. I think we should try as is with the parentheses next to the name, but I'm open to any other suggestion.