Autosave functionality

[waterrmalann]

I think I didn't implement this in the first place due to potential performance implications but it's an extremely necessary feature as people (myself included) often forget to hit the save button. At the very least, a warning prompt to indicate unsaved changes when a user attempts to close the tab would also work.

Autosave timer could be adjusted in the settings panel (not implemented yet).

[maliksenpai]

I will work on this issue