Speed up chapter picker for series with many chapters

[rosszurowski]

This PR introduces a scroll virtualization library to speed up rendering and scrolling performance for the chapter picker.

For long-running series like Bleach or One Piece with hundreds of chapters, it could take a few seconds for the chapter picker to appear as the browser rendered all ~800 rows. With this PR, the browser now only renders the ~20 visible rows at a given time.

Fixes #17

Todo

• [x] Add initial scrolling implementation
• [x] Fix panel scrolling jumpiness on iOS
• [ ] Add volume number headers back to chapter picker
• [ ] Apply windowing to chapter listing on series pages too

[rosszurowski]

Seems like the scroll panel jumpiness was just a bug in a beta version of iOS I was using…