Clean up tutorial docs for installable app pattern with flaskr (#2002)

* Clean up tutorial docs for installable app pattern

- reading sequentially through the tutorial works.
- fixes references to `export FLASK_APP=flaskr.flaskr`

* Fixes titles for each section of flaskr tutorial

* Revert grammar

* Emphasize the Packaging Guide

- adds more general packaging resource
- removes the emphasis put on setuptools

* rephrase and remove note admonitions

- expanded on few points
- removed note blocks, they are unneccessary

* Remove note about reinstalling to update cli

- I had mistakenly thought it was necessary to
  re-install the app to update the cli.
- the `--editable` flag detects the change and
  the cli updates without issue.

docs/tutorial/setuptools.rst

@@ -1,89 +0,0 @@
-.. _tutorial-setuptools:
-
-Step 3: Installing flaskr with setuptools
-=========================================
-
-Flask is now shipped with built-in support for `Click`_.  Click provides
-Flask with enhanced and extensible command line utilities.  Later in this
-tutorial you will see exactly how to extend the ``flask`` command line
-interface (CLI).
-
-A useful pattern to manage a Flask application is to install your app
-using `setuptools`_.  This involves creating a :file:`setup.py`
-in the projects root directory.  You also need to add an empty
-:file:`__init__.py` file to make the :file:`flaskr/flaskr` directory
-a package.  The code structure at this point should be::
-
-    /flaskr
-        /flaskr
-            __init__.py
-            /static
-            /templates
-        setup.py
-
-The content of the ``setup.py`` file for ``flaskr`` is:
-
-.. sourcecode:: python
-
-    from setuptools import setup
-
-    setup(
-        name='flaskr',
-        packages=['flaskr'],
-        include_package_data=True,
-        install_requires=[
-            'flask',
-        ],
-    )
-
-When using setuptools, it is also necessary to specify any special files
-that should be included in your package (in the :file:`MANIFEST.in`).
-In this case, the static and templates directories need to be included,
-as well as the schema. Create the :file:`MANIFEST.in` and add the
-following lines::
-
-    graft flaskr/templates
-    graft flaskr/static
-    include flaskr/schema.sql
-
-At this point you should be able to install the application.  As usual, it
-is recommended to install your Flask application within a `virtualenv`_.
-With that said, go ahead and install the application with::
-
-    pip install --editable .
-
-.. note:: The above installation command assumes that it is run within the
-    projects root directory, `flaskr/`.  Also, the `editable` flag allows
-    editing source code without having to reinstall the Flask app each time
-    you make changes.
-
-With that out of the way, you should be able to start up the application.
-Do this with the following commands::
-
-    export FLASK_APP=flaskr.flaskr
-    export FLASK_DEBUG=1
-    flask run
-
-(In case you are on Windows you need to use `set` instead of `export`).
-The :envvar:`FLASK_DEBUG` flag enables or disables the interactive debugger.
-*Never leave debug mode activated in a production system*, because it will
-allow users to execute code on the server!
-
-You will see a message telling you that server has started along with
-the address at which you can access it.
-
-When you head over to the server in your browser, you will get a 404 error
-because we don't have any views yet.  That will be addressed a little later,
-but first, you should get the database working.
-
-.. admonition:: Externally Visible Server
-
-   Want your server to be publicly available?  Check out the
-   :ref:`externally visible server <public-server>` section for more
-   information.
-
-Continue with :ref:`tutorial-dbcon`.
-
-.. _Click: http://click.pocoo.org
-.. _setuptools: https://setuptools.readthedocs.io
-.. _virtualenv: https://virtualenv.pypa.io