fixed showing speaker's view with timings/pacing while serving the presentation from the file system

Added programatic support for custom key bindings with optional descriptions to be added to the help screen

When a slide has several fragments it could be convenient to define a note for each of them. In this case we need to show only this specific note defined in a fragment and not others. General note of a slide shouldn't be also shown, as a more specific one should have greater relevance in this case.

It would be nice if we could define a custom notes.html file.

Actually, I'm used to compile my js files before releasing my app and, using selectors like `script[src$="notes.js"]`, doesn't work :(

So, what do you think about it?

Its was impossible (at least for me) to keep the windows in sync without bloating the code too much.