Improve election.transform

[pforero]

Currently the election.transform works with very simple inputs. Two political parties and a weight.

1. It will be better if the input of the political parties is by name, not code

2. For future more complex transformations, a different method to input the transformations could be better. Try to implement this new transformation method, even if it only works for today's simple case

[pforero]

First point done in #30