Further refactoring to enable row reordering

Related to #157 (closed)

Here, the rows are assigned dynamically if not set beforehand.

Should check that the start times are in order.

b_asic/_preferences.py

@@ -3,3 +3,5 @@ EXECUTION_TIME_COLOR = (255, 100, 66, 200)
 SIGNAL_COLOR = (0, 0, 0)
 
 SIGNAL_LINEWIDTH = 1.0
+
+OPERATION_GAP = 0.5