Bug 36894: Mobile device detection for third parties

Introduces configuration setting $wgMFAutodetectMobileView which, if set to
true, allows to display mobile content dynamically without the need to rely on
Squid ACLs or AMF for detection.

Change-Id: I1dab4d315c9f9f46d38319a3cf8b37e9fd5ff367
Merge "Bug 36894: Mobile device detection for third parties"