Split pandas functions into separate module.

This frees //labm8:sqlutil from the dependency on
//third_party/py/pandas, which is currently broken.

github.com/ChrisCummins/phd/issues/51

notebooks/BUILD

@@ -25,6 +25,7 @@ py_binary(
         "//labm8:labtypes",
         "//labm8:logutil",
         "//labm8:pbutil",
+        "//labm8:pdutil",
         "//labm8:prof",
         "//labm8:sqlutil",
         "//labm8:viz",