Gdbgui

- correctly display `<` and `>` in console widget

- show disassembly when file is unknown or missing
- show new children in expressions widget when they are dynamically added by application (wuyihao)
- suppress nuisance errors when hover variable or fflush command is not found
- improve logic when source code line should be jumped to
- escape brackets in disassembly, and gracefully hide missing opcodes
- update socketio version for more reliable websocket connection

- Show variable values when hovering in source code
- gracefully handle hostname not being present in /etc/hosts when running with remote flag
- Use external state management library (`stator.js`) for client ui