Thoughts on improving serial backend

[haslinghuis]

Some thoughts for improvement. Already different plugins can be swapped with new implementations if needed.

• - reset GUI when connect fails - currently we do not check return value in serial_backend.js
• - look into reducing events - perhaps moving them to serial.js
• - perhaps most protocol logic could be handled by serial.js - reducing redundancy in protocol implementations - after refactoring methods.
• - create helpers for repeated code, for example data format conversions
• - rename port to device
• - rename path to protocol
• - implement connectionInfo / connectionId