client credentials should be optional (fix #759)

client credentials should only be required on token
request

Signed-off-by: Fernando Rocha <fernandogrd@gmail.com>
Complete remove of client checks from oauth2

Signed-off-by: Fernando Rocha <fernandogrd@gmail.com>
Remove client credentials from all OAuth 2 tests
Remove oauth2-provider backends reference from compat.py
Merge pull request #767 from tomchristie/fix-oauth2-token-only

Fix OAuth 2 token only