Add multiple query feature

[smsunarto]

Some organization have multiple organization account. As an example MovingBlocks have,

1. https://github.com/MovingBlocks/
2. https://github.com/Terasology/

Ergo, we should support queries on multiple organization account to accomodate this.

[jayvdb]

I believe that type of query will work 'out of the box' by using multiple user:x which are or'd together.

e.g. GitHub search user:MovingBlocks user:Terasology

This should also work in the tool, but for me the same parameters only show Terasology issues. I slightly suspect that this is due to (low number of) API results being skewed, or a bug somewhere, and not that we dont need multiple GitHub queries for multiple orgs.
Reason is that user:cadasta user:kobotoolbox shows issues from both orgs.