Add chapter skipping support to exoplayer client

[CeruleanRed]

Changes
Added buttons to support chapter skipping in the exoplayer client. Buttons are only present if chapters actually exist on the file being played. Button behaviour was modeled on how the web client works (e.g. the 10s interval in which going back a chapter results in going to the previous chapter, instead of starting the current one at 0)

Images

(Ignore the video quality, it's trying to software decode AV1 on the emulator)

Extra comments

• Currently when hiding the skip chapter buttons, there is a slight lag until the buttons disappear due to having to check if chapters exist, which can only happen when the media is loaded. Any alternative that improves this would be welcome.
• The "watched" status of the chapter markings only updates after the user has let go of the thumb when scrubbing

Fixes
#155