Added export to file feature

Added abstract class Model

Signed-off-by: Ricardo Leitão <ricardo7rl@gmail.com>
Added application class

Signed-off-by: diogorosa <diogo.m.c.rosa@gmail.com>

Added to CSV format for inbox messages

Function creates CSV file in sdCard root
named messages.csv

Signed-off-by: diogorosa <diogo.m.c.rosa@gmail.com>

Missing models an layouts not included in last commit

Signed-off-by: diogorosa <diogo.m.c.rosa@gmail.com>