DisplayRoosterActivity updated

DisplayRoosterActivity contains some code
to cut the source html from the time table into
an array containing lists with the courses for 1 certain
day. Next step is to create warning messages like "next
course: the string in the list" in ... minutes (with settable
time to warn in advance in the settings menu)

Check comments in code for better understanding! code should
also get replaced to its own class.