Stop Points, High-Contrast, Update notification (bugfix), Android Q fixes.

Fix a number of accessibility issues and some potential crashes shown by automatic testing.
Add a hint on the SECOND time playback is started about the existence of the on-screen volume and speed controls.
Don't do "Button Delay" at startup and when returning from Settings.
Make Simple Kiosk work on Android 10, although it's not recommended because it still is (unfixably) ugly. Make App Pinning more attractive by getting rid of the "Got It" message on Pie and above. Pinning (where available) is the best choice if not using Full Kiosk. Update web page to reflect these changes.
Fix URLs in dialogs to be clickable. Housekeeping in handling the path to the website. Improve error handling if connection to Samples Download website fails.
Fix unzip of books when zip file doesn't contain explicit directory entry. Handle file renumbering when more than 100 files, separate handling of audio files and directories to avoid renumbering unnecessarily.