Update monodepth_simple

[IbrahimOmar91]

Here the list of all Changes:

• Changed default encoder to 'resnet50-forward'
• Fixed calling MonodepthModel function by adding 3 None parameters that were required to run properly
• Changed all scipy image functions that aren't working to cv2 functions (imread, resize)
• Changed old 'disp_left_est' to 'invDepth_left_est'
• Updated Params list adding (lidar_weight = 15.0, do_gradient_fix = True) which have no effect on the result but required to run properly