[config] config file can be registered too

Dump/register also works with config files. Preparing to implement
support for providers with dynamic structure defined by config file.

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[config] changing config file extension

.scm is extension for Scheme, taking into account nothing prevents from
creating providers written on any language, it is better to have generic
.conf extension for configuration files because extension now defines
behaviour of dump/register

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
link with cor library properly

Signed-off-by: Denis Zalevskiy <denis.zalevskiy@jolla.com>
[tests] improve tests reliability

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