[Feature Request] Persisent Queue

**Is your feature request related to a problem? Please describe.**
A clear and concise description of what the problem is. Ex. I'm always frustrated when
***Persistent Queue is simply having the queue remain after a restart or shutdown of the bot***

**Describe the solution you'd like**
A clear and concise description of what you want to happen.
***Persistent Queue could be a something you enable in config.txt file and would keep the queue after a restart of the bot or if a bot shutdown occurs due to a crash or error***
**Describe the basic flow/steps of using this feature**
How this feature would be used:
1. ***Set persistent_queue=true in config.txt***
2. ***play (URL_HERE or SONG NAME HERE)***
3. ***if bot crashes shuts down or restarts it would auto rejoin the voice channel it was in before crashing, shutdown or restart etc etc***
4. ***upon rejoin it starts where it left off and starts with the last song it was playing***

**Additional context**
Add any other context or screenshots about the feature request here.

**Have you confirmed that this idea is not already described here?**
https://github.com/jagrosh/MusicBot/projects/1
***I have seen a `remember queue on exit` entry however I was unable to see how it would continue the queue upon restart so this is more to propose a way in which that may function or work***

Start with the config.txt setting and the play command flow described in the issue, then trace how the queue and voice-channel state are handled across shutdown and restart. Define how the last song and queue should be restored after a crash or restart, including automatic voice-channel rejoining; the feature is done when that flow works reliably when enabled.

Written by the indexing model from the issue text.