UI improvements for touch and forward/rewind buttons.

I've increased the size of the pause button so it's easier to tap on touch devices. I've also made a few style changes.

There are also rewind and fast-forward buttons. They each rewind/fast-forward the audio by 15 seconds. This tends to be the default for podcast apps but there could be a setting (or you could tweak to your liking).

No worries if you don't want these changes. I've been using the app quite a bit on my Firefox phone and wanted to make the changes for myself anyway.