Add CTRL^X COMMAND keymaps

[clcollins]

In order to expand available keystrokes available for commands, and to group related commands, SREPD needs to implement CTRL^X COMMAND support, similar to tmux or nano, or more specifically the strings of commands as in vi.

Done Criteria:

• Pressing CTRL should begin a keymsg loop separate from the main loop, awaiting matching input.
• A matching key command should do the same, looking for a final keypress
• Related commands should be grouped under the first CTRL+X keypress, (X being a placeholder here)

Eg:

• CTRL + o (open browser ...)
• CTRL + o + p (open pagerduty incident in browser)
• CTRL + o + s (open SOP in browser)