Added and started the FindDueActivityForFriend screen, this screen will
display all the activities that this friend still has to pay for, and
the amount due for each of these activities. it might also later have a
small button next to each of these activities to directely pay for each
of them from your account but I am as of now unsure if I will implement
that, also added 2 methods to the com class that will be used, one
returns a string array that holds all the activities of a certain friend
and a second one simply counts how many entries there are in a array,
this is used to check if the friend is part of any activities