Update minitwit & improve testing for examples (#1954)

* Update minitwit & improve testing for examples

* Related to #1945
* Re-works minitwit to be installed and run as:

    pip install --editable .
    export FLASK_APP=minitwit.minitwit
    export FLASK_DEBUG=1
    flask initdb
    flask run

* added flaskr and minitwit to norecursedirs
  * tests not properly run when using pytest standards
  * see: http://stackoverflow.com/questions/38313171/configuring-pytest-with-installable-examples-in-a-project
* Both flaskr and minitwit now follow pytest standards.
* Tests can for them as `py.test` or `python setup.py test`

* Update minitwit readme

* updates the instructions for running

* Fixes for updating the minitwit example

- This reverts the changes to the *docs/* (I will file separate PR).
- Running the app is now: `export FLASK_APP=minitwit` & `flask run`
  (After installing the app)

* Remove unnecessary comma from flaskr/setup.py

examples/flaskr/tests/context.py

@@ -1,6 +0,0 @@
-import sys, os
-
-basedir = os.path.dirname(os.path.abspath(__file__))
-sys.path.insert(0, basedir + '/../')
-
-from flaskr import flaskr

examples/flaskr/tests/test_flaskr.py

@@ -9,11 +9,11 @@
     :license: BSD, see LICENSE for more details.
 """
 
-import pytest
 import os
 import tempfile
+import pytest
+from flaskr import flaskr
 
-from context import flaskr
 
 @pytest.fixture
 def client(request):