[Building Sakai] Link to mobile portal from /portal?

[Silverio, Gonzalo]

Please see https://jira.sakaiproject.org/browse/SAK-19787

At issue is the following flow:

1) User with a mobile device visits the portal and is redirected to the mobile portal.
2) User then clicks the "Switch to Full View" link.
3) In the nightly Sakai there is a footer link back to the mobile version, but we are trying a soft roll out, and do not want to advertise it, and that link is very small in any case. 

So propose to add to the standard portal a more visible link to the mobile version that will only be visible to mobile devices. This would be conditional on a sakai.property, defaulting to false.

Thanks.

	- Gonzalo