Update the IDEF0 A1 diagram (#319)

Update the IDEF0 A1 diagram (#319)

Update the IDEFO A1 diagram: connect backend by Model IR

This commit updates the IDEF0 A1 diagram by adding new connection
from activity block 2 "Import NN model" to activity block 5
"Code generation" by the Model IR. It means that the backend is
able to use the Model IR to produce some output.

Also, it fixes naming of activity boxes.

Signed-off-by: Sergey Vostokov <s.vostokov@samsung.com>