[New feature] Auto copying keymap.rb to the partner half of the split-type

[hasumikin]

Condition

• Split-type

Flow

• Overwriting a keymap.rb happens on the anchor
• Anchor pings a special signal to the partner in order to start copying the keymap.rb
• Both halves switch into XMODEM (or something like that) mode
• Anchor transfers the keymap.rb (or compiled VM code) to the partner
• Partner saves the keymap.rb file in the flash
• Partner sends a signal to finalize the flow
• Both halves switch back to keyboard mode and reload the new keymap

Consideration

• Are there cases where a user wants to have a different keymap on the partner half?