Add unit tests for facebookapps.decorators

Tests for facebook_locale handle bad locale from Facebook (empty or unsupported), already using Facebook's locale, redirecting to Facebook's locale and preserving GET parameters. To pass test, request is no longer sent to get_best_locale function and ? is only appended to locale redirect URL if query string is present.

CONTINUE HERE Test facebookapps' extract_app_data decorator
Add unit tests for facebookapps.views

Tests for tab_redirect view handle FACEBOOK_TAB_URL lazy setting, normal HTTP header redirect to tab, JavaScript redirect, correct HTTP header for iframe usage and converting GET query string into a Facebook app_data query string. To pass the tests, fixes string interpolation of the FACEBOOK_TAB_URL setting for Python 2.6 and only appends ? to URL if a query string is present.

Tests for Download Tab views handle normal HTTP request and check for OK response code, download button selector and JavaScript hooks. Also check for HTTP header for iframe usage.

Adds assertion to TestCase for verifying iframe HTTP headers.
Implement Download Tab copy changes

Also adjust styles for copy changes.
Center Download Tab features list
Fix PEP 8 and Mozilla Web style issues

Fixes several lines that were over 79 characters, separates import blocks in facebookapps.views and removes unused import in facebookapps.models.