Add global hotkeys for Plover functionality

[nsmarkop]

Summary

General Plover functionality like reconnecting the machine does not have a way to trigger it globally and other functionality like enabling / disabling Plover is tied to strokes. It would be convenient to be able to perform some of these Plover actions with global keyboard hotkeys that work without having Plover focused or requiring a machine to be connected for stroke input.

Reproducing

An example of a reconnecting MIDI workflow:

1. Plug in machine
2. Start Plover
3. Type
4. Unplug machine
5. Plug machine back in
6. Try typing - nothing comes out
7. Find the main Plover window and click reconnect

Plover Version

Running from source - d5c8e45.

System

Windows 10

[Nord204]

Whenever I lock my PC and then unlock it, I have to click the refresh button in Plover regardless of whether I'm using Keyboard or MIDI. Such a hotkey would likely have to be a keyboard shortcut and not a chorded command (since Plover isn't recognizing your 'machine'), but this would make using Plover smoother.

[mulka]

Some things I found online that may help with implementing this: https://stackoverflow.com/questions/35564502/c-qt-global-hotkeys https://github.com/falceeffect/UGlobalHotkey https://stackoverflow.com/questions/23193038/how-to-detect-global-key-sequence-press-in-qt

[Peeja]

Also, a QMK board (or another similarly reprogrammable machine), could be configured to automatically send the refresh command keystroke when initially powered or when entering a serial steno mode.

[user202729]

The underlying issue can also be resolved by having Plover auto-reconnect the machine. (see #1054.)

[xsrvmy]

Here's another reason: If you are toggling plover when it is disabled using the keyboard as the steno machine, it dumps content onto the screen. If you fail to focus on a text field before doing this, you end up sending the keys erfvlo followed by 6 backspaces, which may trigger unintended actions.