Add mobile toolbar with Ctrl, Esc, and arrow key buttons

[hanbeex]

Summary

• Adds a toolbar with Ctrl, Esc, and arow key buttons for better support on mobile / touch devices where physical keys are unavailable
• Toolbar is positioned on left side of the terminal
• Ctrl button toggles a mode that intercepts the next keypress and sends it as a Ctrl + key combination. (For example press Ctrl button on the toolbar and then press the 'c' key to use the Ctrl + c key or ^C signal)

[zhengqunkoo]

As a user of ttyd on mobile, I'd like to see this get merged into mainline.

Also, taking reference to Termux and Google Cloud SSH Console, we should also provide more function keys: ESC TAB HOME CTRL ALT END PGUP PGDN

[hanbeex]

Also, taking reference to Termux and Google Cloud SSH Console, we should also provide more function keys: ESC TAB HOME CTRL ALT END PGUP PGDN

Yes! that's actually on my todo list. For now ESC, CTRL, and arrow keys are on top of my list because i think they're the most essential