Move towards toplevel CMakeLists.txt

Change-Id: I2083e87192a796bad6573d991ce18d3bc6de8564
Reviewed-on: http://review.couchbase.org/28728
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>
Tested-by: Trond Norbye <trond.norbye@gmail.com>