feat(windows): make hints auto-dismiss and less obtrusive

**Is your feature request related to a problem? Please describe.**

The hint messages in Keyman are kinda obtrusive. You have to close them by hand, and the "don't show again" checkbox is a pain.

**Describe the solution you'd like**

The hints certainly are useful for new users. But we can make them less obnoxious:
1. It would be nice to have the hint be a small window that appears above the notification area (for default taskbar placement).
2. It shows for a few seconds and then automatically disappears
3. A button "Don't show again" is available on the hint that both dismisses the hint and also does what it says -- stops the hint showing again.

---

**Keyman for Windows/macOS/Linux:**
- OS: Windows
- Keyman version: 14.0