v1.3.0 Release

• #104: ServiceGenerator supports a prefix to put on the #import lines to support custom installs/setups of the source.
• #115: Use forward declaration for some types to reduce imports needed in headers. This removes the need need for user_target_xcconfig in the podspec.
• #128: Tweak the naming of the OAuth2 Scope constants. They common case should be no change, but it now should detect collisions and try generating longer constant names to avoid them.
• #130: Dropped the use of pod_target_xcconfig in the podspec, and instead the sources try to detect this via the common COCOAPODS symbol.
• Updates the generated sources for the services and includes several more.
• The gtm-oauth2 sources are no longer bundled into the Framework generated by the checked in Xcode project as projects should have migrated by now.