Python pip (macOS support)

Created a new snowblock for pip (1) containing the

* `requirements.iceowl.txt` file (2) to track installed packages (3) and
their versions of the `iceowl` host and . See the requirements.txt file
format documentation (4) for details.
* `pip.conf` file (5) for user specific configurations.

References:

  (1) https://pypi.org/project/pip
  (2) https://pip.pypa.io/en/latest/user_guide/#requirements-files
  (3) https://packaging.python.org/tutorials/installing-packages/#requirements-files
  (4) https://pip.pypa.io/en/latest/reference/pip_install/#requirements-file-format
  (5) https://pip.pypa.io/en/stable/user_guide/#config-file

Related to epic GH-131
Closes GH-141

snowblocks/pip/pip.conf

@@ -0,0 +1,12 @@
+# Copyright (C) 2016-present Arctic Ice Studio <[email protected]>
+# Copyright (C) 2016-present Sven Greb <[email protected]>
+
+# Project:    igloo
+# Repository: https://github.com/arcticicestudio/igloo
+# License:    MIT
+# References:
+#   https://pypi.org/project/pip
+#   https://pip.pypa.io/en/stable/user_guide/#config-file
+
+[global]
+timeout = 60

snowblocks/pip/requirements.iceowl.txt

@@ -0,0 +1,26 @@
+# Copyright (C) 2016-present Arctic Ice Studio <[email protected]>
+# Copyright (C) 2016-present Sven Greb <[email protected]>
+
+# Project:    igloo
+# Repository: https://github.com/arcticicestudio/igloo
+# License:    MIT
+# References:
+#   https://pypi.org/project/pip
+#   https://packaging.python.org/tutorials/installing-packages/#requirements-files
+#   https://pip.pypa.io/en/latest/reference/pip_install/#requirements-file-format
+#   https://pip.pypa.io/en/stable/user_guide/#config-file
+
+# +------+
+# + Core +
+# +------+
+
+# The base tool to create isolated Python environments.
+virtualenv
+
+# +------+
+# + Apps +
+# +------+
+
+# Required by the custom hooks of the "taskwarrior" snowblock to interact with Taskwarrior API.
+# See https://github.com/arcticicestudio/igloo/tree/develop/snowblocks/taskwarrior for details.
+taskw

snowblocks/pip/snowblock.json

@@ -0,0 +1,21 @@
+[
+  {
+    "clean": ["~/.config/pip"]
+  },
+  {
+    "link": {
+      "~/.config/pip/pip.conf": {
+        "create": true,
+        "force": true,
+        "path": "pip.conf"
+      },
+      "~/.config/pip/requirements.txt": {
+        "create": true,
+        "force": true,
+        "hosts": {
+          "iceowl": "requirements.iceowl.txt"
+        }
+      }
+    }
+  }
+]