Add ability to map hostname to ideas portal URL Merged

There should be a way to map a client's (sub) domain name to the client's ideas portal.

For example, currently you can specify a portal URL like somecompany.ideas.aha.io, but I also want my own sub-domain, ideas.somecompany.com, to map to my ideas portal.

For a working example, see how Zendesk provides a "Host mapping" setting.