Keyboard Shortcut of hypothes.is interfere with keyboard shortcut of pdf.js

Some [Shortcuts of Pdf.js](https://github.com/mozilla/pdf.js/wiki/frequently-asked-questions#faq-shortcuts) overlap with shortcut of [hypothes.is](https://web.hypothes.is/help/keyboard-shortcuts-for-hypothesis/). For example, `h` trigger both hand mode and highlight.