CMake: Use OBJECT targets and build static library

This makes management of individual library components easier by
removing the intermediate "STATIC" targets for the sub components and
converting them into pseudo-targets via a so-called cmake "OBJECT"
library (see http://www.cmake.org/Wiki/CMake/Tutorials/Object_Library).
This allows quicker build times and less platform specific nuances of
using static libraries.

Additionally, this fix also now makes a dedicated couchbaseS static
library for use by tests, avoiding the need of exporting dozens of
symbols just so they can be used by the tests (in this case, they are
just linked statically with the static library).

Change-Id: If73208c8ad499f8f41d63b32b995a3359f16db01
Reviewed-on: http://review.couchbase.org/41615
Tested-by: Mark Nunberg <mnunberg@haskalah.org>
Reviewed-by: Sergey Avseyev <sergey.avseyev@gmail.com>