Add the ability to play audio files.

Add a slider to seek through an audio file.

Add play/pause and mute/unmute buttons for audio files.

Note: This is a continuation of a mistakenly closed PR:
Ref: TagStudioDev#529

While redoing the changes, I made a couple of improvements.
When the end of the track is reached, the pause button will
swap to the play button and allow the track to be replayed.

Here is the original feature request:
Ref: TagStudioDev#450

* feat: Audio Playback

Add the ability to play audio files.

Add a slider to seek through an audio file.

Add play/pause and mute/unmute buttons for audio files.

Note: This is a continuation of a mistakenly closed PR:
Ref: #529

While redoing the changes, I made a couple of improvements.
When the end of the track is reached, the pause button will
swap to the play button and allow the track to be replayed.

Here is the original feature request:
Ref: #450

* fix: prevent autoplay on new track when paused

* refactor: Add MediaPlayer base class.

Added a MediaPlayer base class per some suggestions
in the PR comments. Hopefully this reduces duplicate code
between the audio/video player in the future.

* refactor: add controls to base MediaPlayer class

Move media controls from the AudioPlayer widget
to the MediaPlayer base class. This removes the need
for a separate AudioPlayer class, and allows the
video player to reuse the media controls.

* fix: position_label update with slider

Update the position_label when the slider is moving.

* fix: replace platform dependent time formatting

Replace the use of `-` in the time format since this
is not availabile on all platforms.

Update initial `position_label` value to '0:00'.