Firefox browser uses download profile by default

A few other browser tweaks:
- Moved atexit (and related quit function) from fixtures.browser to utils.browser
- Added docstrings!
- ensure_browser_open now returns the browser is ensures is open, so you don't also have to import browser to use it
- The ability to pass a webdriver class to start() has been removed in favor of centralizing configuration entirely in env.yaml
Added ipython, pyzmq & tornado to requirements

Not having ipython installed in the virtualenv can make headaches.

ipython also does not list its dependencies - pyzmq and tornado, so they had to be added too.
Merge pull request #380 from weissjeffm/master

Fix empty credential on cloud provider discovery
Merge pull request #367 from seandst/firefox-profile

Firefox browser uses @mfalesni's download profile by default
Browser configuration docs
Merge pull request #368 from seandst/browser-configuration-docs

Browser configuration docs
Removed Assert in favour of assert
Added new mgmt_system docs
Merge pull request #377 from psav/docs_update

Added new mgmt_system docs
Allows txt and csv to download without confirm
Merge pull request #381 from psav/fix_txt_csv

Allows txt and csv to download without confirm
Merge pull request #382 from psav/remove_Assert

Removed Assert in favour of assert
Add zmq devel package to allow zeromq to install
requirements has some hints for devel packages now
Merge pull request #383 from seandst/origin/ipython-requirements

Added ipython to requirements
sphinx-apidoc now generates module docs
Update docs to work better with sphinx-apidoc

Generally, this means removing module name headings, as apidoc already does that.
While I was in here, I also opportunistically linted and clarified some things
Move examples into their respective docstrings

a.k.a. "The one that psav might not like"

Having separate sections for the examples, particulary where the example
wasn't on the same page as the code documentation (accordion, toolbar),
isn't as handy as having the usage right next to the signature, and
Args/Returns/Raises blocks. This was made comical by using the
sphinx-apidoc generator.
Merge pull request #306 from seandst/docs-docs

Docs craziness...
Added modules generation files to gitignore