frontend: exclude class is too big error for AppErrors

Findbugs complains that AppErrors class is too big for analysis. We
want this class to contain all the errors, and there are lots of them -
so for now we should ignore that error for this class.

Change-Id: I1e7e2d1f39513112ccf6131db609d39839bdcb8d
Signed-off-by: Arik Hadas <ahadas@redhat.com>