Make bidpom pip installable

These changes allow us to install bidpom using pip from a branch/tag in the bidpom repository. Sorry for the size of the pull request but really all that's happening here is:

1. Change the structure of the repo so the package files are in a subfolder called `browserid`.
2. Because of the structural changes, change the tests to find the packages that they import (e.g., `BrowserID`, `pages.sign_in`, etc.).
3. Create a `setup.py` file that allows the package to be installed.

The tests for bidpom pass [1], and I also did a test with Moztrap-tests [2] and it passes with the new structure, and using a pip installable package instead of a submodule. I didn't have to change any of the code for Moztrap-tests, but I did have to change the `requirements.txt` file and also I removed the git submodule [3].

Please review this pull request and provide your feedback. I believe that we can merge this if we like, and still keep all of the sites using the submodule for now, as they will all be pointing to an older commit. We can then convert each of the sites to use the package in a similar way to what was done in [3].

We could either point the projects that use this to the master branch, or, as @davehunt suggested, we could use a tag.

[1] http://qa-selenium.mv.mozilla.com:8080/view/BIDPOM/job/bidpom.stage.pip_installable/1/
[2] http://qa-selenium.mv.mozilla.com:8080/view/MozTrap/job/moztrap.dev.saucelabs.adhoc/43/
[3] https://github.com/mozilla/moztrap-tests/pull/135