Gather symbols in a better way

In #816 all IC symbols were gathered in the same file and collected into a dictionary. This dictionary is useful to make all the symbols available to the code that reads config files. However, the method used to collect them into the dictionary is not the best. As suggested here The main alternatives are:

1. A class decorator that adds every variant of the decorated enum to the dictionary
2. Metaclasses

1 is the most straightforward, but both options should be explored and compared to see which one fits best.