Update src/index.html:Added options to save

Added radio buttons to trigger:
Save to file on debug mode, using encodeURIComponent() and window.open() (works in Firefox and Chromium).
-if there is an encoding key, the encoding function will kick in
Create and open window with a summary/tree of the mindmap (all branches): great for copy-pasting to a presentation!
Create and open window with a summary/tree of the mindmap (only shown branches)
Create and save to file a summary/tree of the mindmap