Move Token and CryptoBackend to common

Move Token and CryptoBackend to common

Both Token and CryptoBackend are small types used on the server, both in
the crypto and the service modules. They are defined in the service
module, and crypto submodules have to include these headers. Other than
that, the crypto module is not aware of the service module, and creating
an unnecessary cyclic dependency here shows up in static analysis.

Since they are minor types which don't contain any logic and are used in
different contexts in different modules, I have moved them to the
src/manager/common directory.

Change-Id: Ifd55ec97173b6e99c9c2fec154803dccfa48a1ae