screen reader alerts for invalid/duplicate keyboard shortcuts (JAWS okay, VoiceOver only input text fields "invalid" message, no distinction with "duplicate")

Conflicts:
	lib/Readium.js
	readium-js
separate keyboard settings code
keyboard validator now correctly handles dual invalid+duplicate cases
submodule update
2-pass duplicate search
JAWS screen reader a11y fix: tabs are now buttons instead of links, add-epub-dialog buttons have correct role
Merge remote-tracking branch 'origin/develop' into feature/continues_scroll_view_3

Conflicts:
	css/viewer.css
	lib/ReaderSettingsDialog_Keyboard.js
	templates/add-epub-dialog.html
	templates/settings-dialog.html