Add a "Theme" option to choose between a dark and light theme.
The light theme uses the colors of the dark theme with the luminance
inversed.
The reloading after a configuration change is changed slightly:
- Special handling is needed when the Theme is changed (recreate the views)
- The default implementation of 'onConfigurationChanged' is used
Which triggers more refresh (but don't recreate the views)
- 'onCreateInputView' is no longer needed
