Support for external keyboard shortcuts

Currently, Simplenote for iOS does not support keyboard shortcuts when an external keyboard is connected (to an iPad, for example). Suggestions for external keyboard shortcuts include:

Cmd N (new note)
Cmd P (print)
Shift Cmd C (checklist)
Shift Cmd E (export notes)
Cmd F (search notes)
Cmd = (zoom in)
Cmd - (zoom out)
Cmd 0 (actual size)
Option Cmd L (light theme)
Option Cmd D (dark theme)
Cmd Del (send note to trash)
Shift Cmd Del (empty trash)
Option Cmd P (publish note)
Option Cmd C (share note, collaborate)
Shift Cmd P (pin note)
Shift Cmd M (convert to markdown)

As is standard for other iOS apps, holding down the Cmd key would show the keyboard shortcut options.

The issue names no files, tests, or entry points. Start by locating the iOS note actions and keyboard-command handling, then map the requested shortcuts to those actions. Done means the listed commands work with an external keyboard and holding Cmd displays the available shortcuts.

Written by the indexing model from the issue text.