adding APIs for app test user.

[theeluwin]

This commit is sample implementation of #96. Since TestGetAppAccessToken from test/test_facebook.py does not guarantees a valid app access token, how should I write meaningful test codes?

[martey]

Since TestGetAppAccessToken from test/test_facebook.py does not guarantees a valid app access token, how should I write meaningful test codes?

TestGetAppAccessToken does not explicitly validate the app access token to ensure that it is valid. If get_app_access_token is returning invalid access tokens, TestFQL will also fail.

I am not sure some of the docstrings are actually useful (e.g. it's obvious that the delete_test_user method deletes a test user) and some of the information looks wrong (the methods will return the response from the GraphAPI if they succeed, not True).

[martey]

In order to release 1.0.0 as soon as possible, I am moving this to the 2.0.0 milestone. This isn't a reflection of the quality of your pull request, but of the lack of free time I currently have to devote to this project.

[theeluwin]

Got it. Thanks. But actually, I still feel sorry for quite poor quality of my PR, while still not sure how to improve it.