When viewing a conference, the Instance Name in the header points to
/organizations. On the organizations index, there's a button to see
conferences, but it does nothing. This makes it easy for public users to
get lost.
This commit:
* Adds a function to the organizations controller to show child
conferences
* Adds a public permission to see conferences through an organization
* Represents a subset of conferences, reusing conferences/index view,
for the organization