applets/keyboardlayout: use static text to describe display options

Currently, the Keyboard Layout widget's config window tries very hard to
be clever, by showing text or the flag for the current language as the
display options. Unfortunately this cleverness comes at the expense of
introducing bugs:

1. By forcing the text to be uppercase, the text display no longer
   reflects the reality of what the text will look like in the applet.
2. By showing the current layout's actual flag, the display will look
   broken if the current layout does not set a flag.
3. Using dynamic text and icons here in general is confusing and
   violated the HIG which counsels to use static text for options.

Let's go back to boring static text which always works.