gtk3_4 : adds commentary to add method in GtkContainer

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
gtk3_4 : Add method remove_widget to GtkContainer

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
gtk3_4 : Add getter for resize_mode in GtkContainer

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
gtk3_4 : Add setter for resize_mode in GtkContainer

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
gtk3_4 : Add get_child_at(left, top) in GtkGrid

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>
gtk3_4 : Add insert_row and insert_column methods to GtkGrid

Signed-off-by: Romain Chanoir <chanoir.romain@courrier.uqam.ca>