KA Lite browser test framework

This branch contains test tools and test, using selenium-based browser tests.  All browser tests require an active display.  There are basic registration/login tests for the main and central servers.

Most of the code is in developing useful wrappers around selenium, and a test-case syntax.

@gimick your feedback about the test tools and particularly the developed syntax / readability of the "main" app's browser testcases (see kalite/main/tests/browser_tests.py) would be most welcome.

Please also notice that the case_free_usernames branch will implement tests using this library, and so will be dependent on this code.