[server] Provider inherits statefs_server directly

g++-4.6 with -O2 optimizes something in a way curiously recurring
template pattern works wrong and memory corruption occurs. So,
just implementing logic inside Provider class

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
check is loader exist

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[service] requires dbus.socket

While statefs itself has not any dependencies on d-bus, Some providers
need it and it is just simplier to add dependency on d-bus startup until
I'll found not so ugly way to solve the issue. Later I think there will
be a separate statefs service/instance for each provider

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[config] process using loader

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[inout] implementation of inout loader

Implementation of inout/mirror loader. This loader uses statefs
configuration files as a source of information to create input and
output namespaces with data written to files in the input namespace just
appeared in correponding files in the output namespace

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[doc] inout documentation, package is renamed

Added InOut loader documentation, package is renamed from
statefs-provider-doc to statefs-doc

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>