add some comments to structs

Signed-off-by: Lehner Florian <dev@der-flo.net>
add some comments to card.c

Signed-off-by: Lehner Florian <dev@der-flo.net>
add some comments to ContactCards.c

Signed-off-by: Lehner Florian <dev@der-flo.net>
add some comments to gui.c

Signed-off-by: Lehner Florian <dev@der-flo.net>
add some comments to neon

Signed-off-by: Lehner Florian <dev@der-flo.net>
add some comments to sqlite

Signed-off-by: Lehner Florian <dev@der-flo.net>