Add Global Lock Screen

[aashutoshrathi]

Discussions (might be broken into multiple issues)

• Add the option to enable lock in settings.
• Ask for the PIN to set for the lock screen [also make internet mandatory for this process, or store it safely somewhere offline].
• Map (Ctrl + L) to Lock Globally (maybe By changing the window URL from the main process).
• Add a button to log-off from the app.
• Should we add something to the lock screen? or just input for a password? Or maybe we can add tips like info about features, hotkeys, and tips about using it efficiently. From some JSON file in public.

[mohitkyadav]

In 3rd point why use main process?
The more we are dependent on main process the more it is harder to port it into a web version.