User organization editor

SU's can now edit a user's organization.  Adding an organization
automatically adds the Network role.  Setting the org to no-org(0)
automatically removes the Network role.
Improvements post code-review

* constants are constant
* database stores either 1..N or null for organization
* development version of underscore included
Merge pull request #7 from azavea/topic/user-org-editor

User organization editor