add cython and NumPy back

@kluyvert @danilevc

requirements.txt

@@ -3,6 +3,7 @@ git+file:///gpfs/exfel/sw/calsoft/git/nbparameterise@0.3
 git+file:///gpfs/exfel/sw/calsoft/git/pyDetLib@2.5.3-2.7.0#subdirectory=lib
 astcheck == 0.2.5
 astsearch == 0.1.3
+Cython == 0.29.21
 dill == 0.3.0
 extra_data == 1.2.0
 extra_geom == 1.0.0
@@ -25,6 +26,7 @@ lxml == 4.5.0
 metadata_client == 3.0.5
 nbconvert == 5.6.1
 nbformat == 5.0.7
+numpy == 1.19.1
 prettytable == 0.7.2
 pypandoc == 1.4
 python-dateutil == 2.8.1