Upgrade to official build tools 1.0 and add gradle wrapper.

The wrapper is for people who might be on Windows or not used to a gradle build system. They can just run commands with ./gradlew instead of having to install gradle themselves.
Um. Why would we .gitignore the manifest file? Re-add it.
Remove crashlytics repo - update min API version.
Remove uses-sdk. It is always replaced by the value in the build.gradle file.
Merge pull request #157 from gametimesf/upgrade-tools-1.0

Upgrade to official build tools 1.0 and add gradle wrapper.