Update the group description upon a group change

The group is initially set in PHP. Before this change
it was not updated when a new group was selected, and
the description of the old group was shown.

Now the group description is updated. The changeGroup()
function is changed so now it receives a message object,
which includes the id and the description. The description
is then parsed and updated in the DOM.

The existing calls to changeGroup() are changed
to pass a message object instead of a string.

Change-Id: I13da35cf20d7280e55e327b6a9928df387e80565
Merge "Update the group description upon a group change"