Remove the need for image files in tests.

We use the python unittest class methods to setup the images so they are not
called for every test.
* tests/helpers.py : We add an additional image to the image list
"2013_10_30_06_30_00".
(imgs_common_tsdir): New method that will setup and tear down all images
necessary for the tests
* tests/test_classes.py (TestTimeStreamStr, TestTimeStreamLoad)
(TestTimeStreamImagePathAssing, TestTimeStreamIterByFiles)
(TestTimeStreamIterByTimepoints): Add setUpClass and tearDownClass
class methods.
* tests/test_parse.py (TestAllFilesWithExt, TestGuessManifest, TestGetImage):
Likewise
Merge pull request #153 from Joelgranados/testnoimg

Remove the need for image files in tests.