Fix GlobalTitle caching issues with sandbox/prod

GlobalTitle shares the cache between production and sandbox/preview verify environments. That would be fine if only it didn't cache URLs that are specific to the environment...

Wikia::getEnvironmentName() is the proposed to solve similar issues. Just add it to the memcached key and you should be safe. Please share any comments on that idea.

/cc @Wikia/platform-team @bognix @kvas-damian 
These are defined in config/Environments.php but not in a good way for this kind of thing.  Maybe we should also put them into an array in the config so it's in one place?  like wgWikiaEnvironments?