Hacker's Keyboard v1.40.3 ALPHA

Merge sbeyer's PR #557, adds Settings button and Test field to main activity

Fix the persistent notification to show an icon and work with the new API level 26 requirements.

This is currently published on Play Store as an alpha version. You can opt in for testing here: https://play.google.com/apps/testing/org.pocketworkstation.pckeyboard