lesson <div> - separate lesson type and lesson group
lesson <div> - separate lesson type and lesson group

For instance, a lesson type "Lecture" of group "V2" will be split into
the lesson type text "Lecture", followed by a span of class
`lesson-group` with text "V2". This is to enable the toggling of
visibility of the lesson group in an upcoming patch.

Signed-off-by: Pang Yan Han <22594c345857f664c61cd411f607c4d40a9d4af9@gmail.com>

yanhan/cljs-nusmods,yanhan/cljs-nusmods,yanhan/cljs-nusmods