Options to customize groupId column

[matdurand]

Added a setting to be able to change the groupId column name and return it as part of each object

[mizzao]

Hi @matdurand, can you tell me a little more about your use case for custom _groupIds?

[matdurand]

Hi! I have a existing database, partitioned using a column with another name. Instead of renaming all my documents I would like to be able to specify the name of the column used to partition the data, instead of it being hardcoded to "_groupId".

[mizzao]

I see. Cool!

I haven't had time to maintain this package lately, so I've added you as a collaborator and you can feel free to merge in these changes and any other updates you'd like. If you send me your Meteor developer username, I can give you permission to publish it new versions to Atmosphere as well.

It would be nice if before merging, you could remove the superfluous space added in package.js (squashing the commits) and keep the 2-space convention across files. Also, maybe you can figure out what to add to that file so that the package works properly with Meteor 1.4 and the tests run on Travis.