added dataset for visualization

visualization/data/populations.csv

+,Year,Belgium,Denmark,Netherlands,Sweden
+0,1950,17.278599999999997,8.5627,20.2273,14.0332
+1,1951,17.3564,8.607399999999998,20.528799999999997,14.140799999999999
+2,1952,17.4608,8.6676,20.7642,14.248899999999999
+3,1953,17.555500000000002,8.7386,20.986,14.3429
+4,1954,17.6388,8.811399999999999,21.2307,14.4272
+5,1955,17.7367,8.8784,21.5018,14.5247
+6,1956,17.8477,8.9328,21.7792,14.6314
+7,1957,17.9787,8.9757,22.0527,14.734300000000001
+8,1958,18.1051,9.0302,22.373600000000003,14.8306
+9,1959,18.2072,9.0932,22.6954,14.907499999999999
+10,1960,18.2376,9.1621,22.973399999999998,14.9607
+11,1961,18.331699999999998,9.2338,23.2775,15.0413
+12,1962,18.436799999999998,9.2939,23.6113,15.1232
+13,1963,18.566200000000002,9.3672,23.931600000000003,15.2087
+14,1964,18.7339,9.4404,24.2543,15.3228
+15,1965,18.896,9.516200000000001,24.5893,15.4678
+16,1966,19.015700000000002,9.595,24.9128,15.6157
+17,1967,19.1129,9.6775,25.1965,15.7355
+18,1968,19.179699999999997,9.729700000000001,25.4594,15.8246
+19,1969,19.2252,9.781500000000001,25.7561,15.936
+20,1970,19.275399999999998,9.8576,26.076999999999998,16.085700000000003
+21,1971,19.346600000000002,9.901399999999999,26.3891,16.1967
+22,1972,19.4222,9.9512,26.6567,16.2449
+23,1973,19.4836,10.0152,26.8784,16.2738
+24,1974,19.5131,10.0905,27.0903,16.320700000000002
+25,1975,19.6017,10.108799999999999,27.3328,16.3854
+26,1976,19.6363,10.1451,27.548000000000002,16.4448
+27,1977,19.660600000000002,10.1766,27.7125,16.502899999999997
+28,1978,19.674599999999998,10.2087,27.8837,16.5517
+29,1979,19.6968,10.2336,28.0765,16.587400000000002
+30,1980,19.7103,10.245999999999999,28.2994,16.6209
+31,1981,19.6976,10.243400000000001,28.4942,16.641
+32,1982,19.714599999999997,10.2355,28.625500000000002,16.6503
+33,1983,19.716,10.2286,28.7339,16.658
+34,1984,19.706,10.2232,28.848399999999998,16.6732
+35,1985,19.7165,10.2274,28.9833,16.7008
+36,1986,19.729599999999998,10.2408,29.144199999999998,16.7396
+37,1987,19.7404,10.254,29.3305,16.795699999999997
+38,1988,19.8034,10.2586,29.5202,16.873
+39,1989,19.8754,10.2646,29.698,16.9859
+40,1990,19.934800000000003,10.2798,29.903,17.1173
+41,1991,20.0092,10.3081,30.1391,17.2273
+42,1992,20.0903,10.3404,30.3681,17.3364
+43,1993,20.1674,10.378499999999999,30.5811,17.4373
+44,1994,20.230800000000002,10.4101,30.7657,17.5621
+45,1995,20.2735,10.4558,30.9179,17.654
+46,1996,20.313285999999998,10.523299999999999,31.061,17.6821
+47,1997,20.340452,10.5686,31.2216,17.6925
+48,1998,20.406016,10.602599999999999,31.4146,17.702399999999997
+49,1999,20.452844,10.63822,31.624,17.716102
+50,2000,20.502511,10.674688,31.851039,17.744588
+51,2001,20.573149,10.710163999999999,32.092372999999995,17.792254
+52,2002,20.665584000000003,10.74851,32.297866,17.849916
+53,2003,20.752265,10.774348,32.450617,17.916458
+54,2004,20.842273,10.802354000000001,32.563558,17.987062
+55,2005,20.957247000000002,10.831956,32.64002,18.059144
+56,2006,21.0959255,10.869133999999999,32.692484,18.161009
+57,2007,21.251411,10.91483,32.763406,18.296198
+58,2008,21.419958,10.978044,32.891203000000004,18.439287
+59,2009,21.592997,11.038882000000001,33.060784999999996,18.597040999999997
+60,2010,21.67981,11.087638,33.230799000000005,18.756252
+61,2011,22.001275999999997,11.133712,33.386160000000004,18.898439
+62,2012,22.189700000000002,11.17417,33.509935999999996,19.038762
+63,2013,22.356872,11.217568,33.608877,19.200757
+64,2014,22.454566,11.279437999999999,33.608877,19.392219
+65,2015,,,33.879855,19.392219