Adjust defaults

This MR changes the default values for a number of parameters: the data fraction used for the final cycle (final_data_fraction), the image size, and the flag that determines whether diagonal solutions are applied during imaging (apply_diagonal_solutions). An image padding of 10% was also removed, as WSClean does its own padding internally. A test run (of two selfcal cycles) was done to verify that these new defaults work as expected.