implement new AddPermissionWithContext func within TestSNSAPI

[usererror]

This will add unimplemented functions for the TestSNSAPI interface to make tests pass. If this build passes should I also add the other context funcs?

[coveralls]

Coverage increased (+0.3%) to 40.909% when pulling 16a7e6b on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling 3990588 on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling f341875 on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling 1fac6f5 on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling d5e9463 on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling 876119a on scotts-nyt:master into 12c3a2a on NYTimes:master.

[coveralls]

Coverage remained the same at 40.59% when pulling 9e8d78a on scotts-nyt:master into 12c3a2a on NYTimes:master.

[oliver-nyt]

[jprobinson]

We pulled this in with PR #95