Python 2 to 3 fixes (#1021)

* Fix print statement

* Check if platform starts with linux (could be linux2)

* Various fixes

* Add environment.yml

Author: davidbrochart

environment.yml

@@ -0,0 +1,15 @@
+name: proteus
+channels:
+  - conda-forge
+  - defaults
+dependencies:
+  - proteus
+  - petsc4py
+  - notebook
+  - future
+  - ipyparallel
+  - cython
+  - pillow
+  - pip
+  - pip:
+    - recordtype