Add Quick Actions prototype

This MR adds the prototype of a Quick Actions popup to GitDock.

The Quick Actions can be opened by pressing Ctrl+Alt+G / Ctrl+Alt+P (on Mac: Cmd+Opt+G / Cmd+Opt+P) anywhere in your operating system when GitDock is open. You can search for an action by typing and select one by using the arrow keys (↑ and ↓). An action is executed by pressing Enter. The popup can be closed by switching to a different window or pressing Esc.

On a technical level, this is implemented detached from other GitDock code in src/quick-actions/. The popup is a plain electron window that loads the Quick Actions HTML and some additional data (the user’s top-level groups from the GitLab instance and their username) to display the actions. Actions are registered in the ALL_ACTIONS object with the title and an execute method that is called when the action is executed.

Relates to #26 (closed)

Screenshots

Video demo: https://youtu.be/UctmhfkjStA

Example	Screenshot
No search terms
Opening a group
Creating something new