Whenever the language is changed outside the bar, update the bar
accordingly. Also, when a new language is used, automatically append it
to the list of available languages.
User can now specify a list of languages as parameter (pipe-separated
list). Variants can also be specified by separating language and variant
with a :
For instance: -p layout.lang="us|rs:latin"
Left click moves on to the next language, right click to the previous.
Right now, there are the following caveats:
* The first entry in the list must be the language used when the bar
starts
* kxbd changes outside the bar are not picked up automatically
