Simplifies the logic behind skipping tracks

[iamdb]

This is maintanance work to primarily clean up the skip logic that hadn't been touched and was overly complicated.

In addition...

• adds target state to loading notification for players
• fixes end of stream not going to first track
• fixes some old code around track playing in the player that was functional but incorrect
• adds a loading icon to the tui and changes the web ui notifications so they don't overlap
• has the resume function wait for the player to reach a paused state before seeking to the last saved position.
• fixes the loading state not working in the web ui
• adds a progress bar to the web ui