Add option to disable auto-save and add ability to manually save

[TheDcoder]

Feature Request

Add option to disable auto-save and add ability to manually save.

What problem does it solve?

I like my changes to be atomic, I don't like the fact that each and every change automatically gets written to the disk as soon as it is made.

This would also make any previous versions of the todo.txt in a file sync solution cleaner and easier to navigate.

How does the user interface change to accommodate this request?

1. A new simple option to save the file (File -> Save file (Ctrl + S))
2. A new option in settings to toggle auto-save
3. Some kind of indication that the current todo has been modified (like a star after the file name in the tab)
4. A warning if the user attempts to quit without saving