refactor hash parsing, fixes issue with autoplaying media not starting from internal links on mobile devices

new shortcuts; alt+arrow key skips fragments, shift+arrow key jumps to last slide in the given direction #1105

fixes #2635

The progress bar shows how many slides have been passed in total.
However, when clicking on the progress bar, the target slide is
computed among the subset of /horizontal/ slides.  Thus, when the new
slide is displayed, the progress bar has usually changed to a point
that is unrelated to the clicked one, which I find surprising.

With this change, the target slide is computed from the number of
total slides.  Thus, after a click on the progress bar, the resulting
progress is close to the clicked point, which seems more natural to
me.

There is a small typo in js/controllers/autoanimate.js.

Should read `transition` rather than `transiition`.