shortcuts.js continue #2421 rewrite

[raszpl]

• modular design, shortcuts separated into shortcutsInit shortcutsHandler shortcutsListeners
• listeners installed only if there are shortcuts active
• removing all shortcuts unloads listeners
• removed player hover listener
• rewritten shortcutChapters shortcutTranscript
• renames 'Show chapters Sidebar' 'transcript' to 'Toggle sidebar Chapters' 'Toggle sidebar Transcript'