Cleaning up tests directory

This is my first step towards cleaning up the tests directory a little bit.
These three images aren't supposed to be here, and they shouldn't come back.
Fixes test_optional and test_stereovision breaking

This fixes some tests that were breaking, and also removes a couple of typos.
I also took the liberty of changing some aesthetic stuff, which were non-pythonic.
Adds the /tests/standard folder to .gitignore
Removes test-generated images from repository.
Fixes typo
Moves StereoVision test stuff out of the test root
Fixes test missing stereovision stuff

This fixes one test which also used the StereoVision files. It should probably
be moved to test_stereovision, but whoever put it here must have had a good reason.
Merge pull request #399 from victsou/develop

Cleaning up tests directory. Awesome. Thanks.