always use css transforms for presentation scaling (zoom has too many quirks even if it is slightly sharper on ldpi displays)

.substr() is deprecated so we replace it with .slice() which works similarily but isn't deprecated
Signed-off-by: Tobias Speicher <rootcommander@gmail.com>

fix fullscreen issues; correct size in Safari, auto-focus presentation when entering fullscreen #3080

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