Show the sorting progress

[JRobsonJr]

Is your feature request related to a problem? Please describe.
With our current sorting algorithm, reordering a 100-track playlist can take longer than 30 seconds. Currently, the playlist page only displays a message asking for patience, which doesn't help much:

Describe the solution you'd like
The user should be able to see the percentage of the sorting progress or another kind of component that allows them to predict when the sorting will be over.

Describe alternatives you've considered
It's necessary to keep track of which track is being sorted in a given moment, something that has to be implemented in the sorting algorithm. Display-wise, since we're already using Bootstrap, their progress component could come in handy.