Update Solr install fabric tasks

Update the fabric tasks that install Solr/Jetty to use the Solr
example.

Install the Solr-2155 plugin to the core's lib directory instead
of globally.

Update the Travis build configuration to use this Solr install.
Make package installation tasks able to be run locally
Properly pass the run_local parameter

Pass it as a keyword argument rather than a conditional one
Make Solr core directories as part of Travis install
Pass instance environment variable to Fabric tasks

Pass ``instance`` environment variable to Fabric tasks in the Travis
CI build so the Solr core directories get created correctly.
Reenable Solr Haystack backend

The Haystack backend had been disabled because the Solr install
was broken on Travis.  Now that the Solr install is fixed, try
re-enabling the "real" backend (and running the Solr-specific
tests)
Update to local/remote command execution logic

Factor the logic that selects the local or remote version of functions
like ``sudo()`` and ``run()`` into functions.

Support local execution in the following tasks:

* createdb
* createuser
* install_config
Update requirements file

Update the requirements file for pip

distribute should no longer be required because the virtualenv
should be created with "virtualenv --distribute"

pytz has unconventional versions which causes propblems for pip.
The workaround is to explicitly specify a minimum version.
Debug Solr issues in Travis build

Output the Solr logs if the script fails
Install schema.xml as part of Travis build

The ``install_solr_config`` Fabric task doesn't copy over the
schema.xml file.  We need to do this explicitly in
``scripts/ci_before_script.sh``.
Remove debugging commands from Travis build

Now that the Solr install is working correctly in Travis, remove
debugging commands.  Also, remove stale commands from the Travis
build scripts.
Merge branch 'updated_solr_install' into develop
Activity content type

Create models and admin interfaces for an Activity content type
that describes storytelling activities.

Create a CMS plugin for embedding the activity element into a
page.

Add a template, ``cmsplugin_storybase/activity_plugin.html``,
and LESS stylesheet, ``activity.less`` for the plugin.

Addresses #853
Update changelog to reflect Fabric task updates