Refactoring: make sure row applier is called with context.

When we recover either from a remote source or
from local log file/snapshot, a module "apply row" function
is invoked. Up until now this function
was invoked with a single argument - the row to apply,
and there were no context which would be passed around.

This worked fine as long as fibers were "all inclusive" --
i.e. contained all possible context which a function may need.

Now, when networking API and IO handles are split from
struct fiber, they need to be passed around explicitly,
in particular, into row apply function.

Prepeare the code base for this.