Refs #252: Simplify handler loading

New setting RAPIDSMS_HANDLERS is a list of names of handler
classes to load. The previous settings are deprecated.
stub out 0.15 release notes
Refs #375: Add requests to README

Add the Requests package to the list of dependencies
in the README.
Refs #318: Show inheritance for test classes

This turned out to be much harder than it ought to have been
due to Sphinx. We provider shorter import paths for many of
these classes by importing them to their package's __init__.py
and them importing them from there when we use them. This
confused Sphinx greatly; it could not tell that the two possible
names of a class were the same.

Also, if you add :show-inheritance: to an :autoclass: section,
Sphinx insists that it must find a reference to documentation
for every class in the inheritance chain, or else (since we
build with nitpick mode on), the build fails.

In the end, I wrote in most of the classes' doc strings, things
like "Inherits from <link to class>, <link to class>".
Merge pull request #375 from rapidsms/375-add-requests-to-README

Add requests to list of deps in README
Refs #360: Add contributing example to docs
Refs #333: Add Django messages to base template

* Display messages from the Django messages framework at the top of any
  page that inherits from the RapidSMS base template.
* Send some messages from the test and registration apps.
Refs #360: Mention new doc page in release notes
Merge branch 'develop' into 252-simplify-handler-loading

Conflicts:
	docs/releases/0.14.0.rst
Update version numbers in docs; use import_class instead of try_import
Sketch outline of tutorial
Clearly mark the tutorial as a draft so we can put it on RTFD for comments
First pass at tutorial part 1
Start on tutorial part 2
Refs #252: Add tests, a little more doc
Merge branch '252-simplify-handler-loading' into tutorial

So I can assume the new RAPIDSMS_HANDLERS setting and talk
about that in the tutorial. Much simpler than the old
settings to explain.
Flesh out tutorial 2; still need to check that the examples work
Finish up tutorial02
Start on tutorial03
Merge remote-tracking branch 'origin/333-add-django-messages-to-base-template' into develop