Added New Files created by Crashlytics Plugin

@Crashlytics keeps on updating their gradle [plugin](https://www.crashlytics.com/downloads/gradle) to make life easier. After the recent [August](http://www.crashlytics.com/blog/crashlytics-august-update/) update they added some more flexibility for custom builds. This resulted in some ~~more~~ extra files being generated for the user.  
The `crashlytics.properties` file contains the secret and can [alternatively](https://plus.google.com/+AntonioBertucci/posts/S9krjvXfgfm) contain the apikey to rid your repo of the extra strings file. `crashlytics-build.properties` is updated constantly with info that is (seemingly) useful to someone but has no value in source control.  
These files can be found in multiple locations, hence the `**` to catch all instances of both files.