Add prev/next in volume cover modal to quickly view different covers

[ErikHumphrey]

Self-explanatory.

Mockup

Implementation

• Hide or disable prev if on the first volume
• Hide or disable next if on the latest volume
• Don't make a dropdown menu because that would be an ugly thing to put in the modal that would rarely be used

Extra

Also consider increasing the size of the modal/the volume cover image. On 1920x1080, the volume cover is only about 4.5x larger when enlarged.