Update Mongo version and make version configurable

This pull does 2 main things:

* Updates the version of the embedded Mongo used by the plug-in.  The default production version is now 2.6.1.
* Allow the version of Mongo used to be configured in the build script.  The default value is the current PRODUCTION release.

I also added support for Eclipse to `.gitignore` and `build.gradle` and update the version of gradle used by the wrapper to 1.12.