Expand cities to European cities above 100k population

[mszell]

Inspired by #1
To do:

• Get European city names (not including the transcontinental countries for now: Russia, Kazakhstan, Azerbaijan, Georgia, and Turkey) from https://en.wikipedia.org/wiki/List_of_towns_and_cities_with_100,000_or_more_inhabitants, add them to a new file cities/european_100000pop.csv, like cities/european_capitals.csv. Start by taking the same nominatim_query column as the name column. Also add a new column population with the integer population, so can filter later by size, if needed.
• Double-check using the "Check city boundaries" section in scripts/build_recommends.ipynb that the nominatim_query really correspond to the intended city. If not, try to find the correct nominatim_query using nominatim.openstreetmap.org. If you can't find a working nominatim_query, note it down in Individual city issues for growbikenet #6. Also, while doing all this, also note down in Individual city issues for growbikenet #6 any cities with "weird" boundaries that OSM might provide. Let's define a boundary "weird" if it is not the same as in google maps (to be investigated/fixed at a later time).
• Double check boundaries with @mszell
• Once cities/european_100000pop.csv is ready, create a new csv called cities/european_capitalsand100000pop.csv by merging cities/european_100000pop.csv with cities/european_capitals.csv.
• Run the whole scripts/build_recommends.ipynb script with cityfilename = "european_capitalsand100000pop.csv". This will populate cities/rec_table.csv.

[mszell]

Please also add a column for the country, using alpha2.