DRY
user AFOAuth1Client as superclass
remove gtm-oauth dependency
remove magic numbers
Merge branch 'master' into AFOAuth1Client_subclass

Conflicts:
	XINGAPI.podspec
	XNGAPIClient/XNGAPIClient.m
	XNGAPIClient/XNGOAuthHandler.m
	XNGAPIClientExample/XNGAPIClientExample.xcodeproj/project.pbxproj
fix tests
Merge pull request #5 from toco/AFOAuth1Client_subclass

subclass AFOAuth1Client and get rid of gtm-oauth.