Added a `BOOL` return type to the `engage:` method.
The method now returns whether or not an interaction was successfully found and run.
Fixes IOS-354
Changing the ATEvent monitoring to ATLogError rather than NSAssert.
Merge branch 'Next' of https://github.com/apptentive/apptentive-ios into Next
Updating Engagement Framework Criteria:
Replaced `days_since_install` with `time_since_install`
Added `is_update` for `version` and `build`
Updated test data to use `time_since_install` vs. `days_since_install`
Added tests for `is_update` version and build
Added tests for new Upgrade Message criteria json
Added CodePointInvokesBuild and InteractionsInvokesBuild
Added an API method to set the initial useMessageCenter setting. This will be overridden by the server-based configuration when it is downloaded.
Updated to 1.2.7