Set PROJECT in the topmost CMakeLists.txt

Change-Id: I74ad557c4493e82dc608070ae46dcbe7ba44e96b
Reviewed-on: http://review.couchbase.org/35358
Reviewed-by: Trond Norbye <trond.norbye@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>