Update README.md

Add custom message data to optional section.
Update README.md
Allow EnjoymentDialog to be canceled. Send enjoyment_dialog.cancel Vvent in this case, and set the rating flow State to POSTPONED, just as if the user had tapped "No".
Make RatingDialog also dismissible via back button. Fix problem where on KitKat, rating flow can show up twice.
[#ANDROID-223] Trim Survey text responses
Update README.
Bump to 1.2.4
Merge branch 'master' into ua_integration
Update changelog.
Set version to 1.2.4 in changelog.
Merge branch 'master' of https://github.com/apptentive/apptentive-android
Merge branch 'master' into ua_integration

Conflicts:
	CHANGELOG.md
Bump to 1.2.5