Fix disconnect

[balloob]

• Always fire disconnect event when read loop finishes
• On close, wait till the read loop is finished
• Breaking change: Reset but don't close the serial port on closing ESP Web Flasher. It's passed in in the open state, so it's up to the caller to close the port.

[TD-er]

Hmm this last remark about keeping the serial port open gives me an idea.
Would it be possible to schedule a number of calls to the node after some delay, or maybe even after reading back some specific string?
This would allow to enter some credentials to be sent via the serial port at the initial boot.

[balloob]

Yes, that is possible and that's what we're doing with ESP Web Tools v2. It supports sending credentials using the new Improv over Serial