Standard redirect includes for mobile browsers

[amcclain]

We have a basic $is_mobile variable set in our xh.conf:

xh-nginx/xh.conf

Line 36 in e86974e

map $is_desktop $is_mobile {

It would be helpful to have a standard one-line include we could drop in a location block to use this detection to either a) redirect to '/mobile/' or b) redirect to a very simple but well-formatted HTML page we include in the base image that indicates mobile is not supported. These could be two includes e.g. redirectToMobile and renderMobileNotSupported.