Add captive-portal image

[rgaudin]

We need an image that replicates the hostpost's captive portal, interacting with the host's firewall and redirecting to the appropriate homepage.

[kelson42]

IMO, would be good to have a dedicated repository for the code itself of the captive portal.

[rgaudin]

I agree this is probably best if we want to foster its integration into other's system. That said it may be additional work so we might do it in stages.

[kelson42]

@rgaudin Supportive of investing the time soon.

[rgaudin]

@Popolechien same question as for #7: how much of the UI do you want to keep?

This is just the Apple sample, as it's different accross platforms but you get the idea.

[Popolechien]

We can keep it all.

[rgaudin]

Fixed in a696781