Simplify ENTE and enable new exchanges

[systemcatch]

fixes #1719

Based on the new info provided by Alex I've been able to simplify the parser significantly. All the exchanges bar HO->NI can now be displayed on the map. That one has a bug in the data but since the NI parser provides exchange data anyway it shouldn't be significant.

Output of parsers.

(EM-env) chris@ThinkPad:~/electricitymap$ python parsers/ENTE.py
fetch_exchange(CR, PA) ->
{'source': 'enteoperador.org', 'netFlow': -18.0, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'CR->PA'}
fetch_exchange(CR, NI) ->
{'source': 'enteoperador.org', 'netFlow': 42.9, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'CR->NI'}
fetch_exchange(GT, MX) ->
{'source': 'enteoperador.org', 'netFlow': -147.5, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'GT->MX'}
fetch_exchange(GT, SV) ->
{'source': 'enteoperador.org', 'netFlow': 92.9, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'GT->SV'}
fetch_exchange(GT, HN) ->
{'source': 'enteoperador.org', 'netFlow': 57.4, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'GT->HN'}
fetch_exchange(HN, SV) ->
{'source': 'enteoperador.org', 'netFlow': 68.5, 'datetime': datetime.datetime(2018, 12, 30, 10, 15, tzinfo=tzstr('UTC-6')), 'sortedZoneKeys': 'HN->SV'}

[alixunderplatz]

Checked the directions and flows - perfect! 👍

[corradio]

100 lines of code less! Awesome guys!

[systemcatch]

@alixunderplatz I see you can run python programs now, very nice!

@corradio it was so satisfying deleting all of the spaghetti logic code.