Use a (mostly) hermetic Python interpreter

It still requires python to be installed on the host to run the wrapper
scripts, but it's close to being fully hermetic.

This also requires/enables the following changes, unfortunately all at
the same time:
 * Use a downloaded f2py
 * Use a downloaded scipy/numpy/matplotlib
 * Fix a few things that don't run with the python version in their #!
 * Stop using bazel-generated __init__.py files, because those interfere
   with importing matplotlib nicely

Change-Id: Ife280464613d67cece9587b7d947f0b1d5466d7e
diff --git a/tools/python/BUILD b/tools/python/BUILD
new file mode 100644
index 0000000..2181b31
--- /dev/null
+++ b/tools/python/BUILD
@@ -0,0 +1,9 @@
+py_runtime(
+    name = "runtime",
+    files = [
+        "runtime_binary.sh",
+        "@python_repo//:all_files",
+    ],
+    interpreter = "runtime_binary.sh",
+    visibility = ["//visibility:public"],
+)