Story 141: Set wgMobileDeviceName in a device specific js module

Depends on $wgMFVaryResources = true

Note the name wgMobileDeviceName may change in future but this is
currently set in CentralNotice

Unresolved issue: this must be run before the banner controller - use RL dependencies?

Change-Id: I4f3a43b2172367d03504ee9318d51173f54e1623
Merge "Story 141: Set wgMobileDeviceName in a device specific js module"