Move Utility to a new common static library

Move Utility to a new common static library

Now that csync builds as C++, this will avoid having to implement
functionalities needed by csync mandatorily in csync itself.

This library is built as part of libocsync and symbols exported
through it.
This requires a relicense of Utility as LGPL. All classes moved into
this library from src/libsync will need to be relicensed as well.